Question
I have pots outside with flowers in them. How can I stop the problem of stray cats using them as litter boxes? I don't want to spray or put anything harmful to humans down on the ground becuase I have 2 little boys that are very curious.

Answer
Solutions
I get various requests for methods to keep cats out of gardens, property etc. I am always looking for new ones but here are some that you may want to consider. The best solution is to push for laws that require leashes on all cats. Unfortunately, the cat lobby is extraordinarily powerful. I love cats but I love indoor cats, both of mine are indoor cats! Outdoor cats are responsible for incredible environmental devastation to wildlife populations. It is very sad, but until people put pressure on government officials to crack down on free-roaming cats, I don抰 see the problem going away. Landscape Damage
Cats can be a substantial problem for gardeners and those who love wildlife. Cats and dogs are tough. For some reason the public doesn't believe in leash laws on cats and refuses to enforce the law on dogs. I would suggest a fence for your lawn/garden that is too high for them to jump. I would go up at least five feet. Make it wobbly so they won't want to climb it. You can also try a scare crow water sprinkler. It works by shooting out water when the motion detector is triggered. Since it is a stray, it may be used to water though. Also this technique won't work during the winter if your part of the country experiences freezing temperatures. Otherwise, you will need to remove it or tie your own dog nearby. There is a new product called "Scat Mat". It shocks the animal that stands on the pad. Problem is that you would need a lot of pads. To buy it see below
Don't bother with plants that allegedly repel animals. There aren't any that would be fool proof because all a free roaming mammal has to do is walk past it up wind. But if you insist on using some here are a few to try. (WARNING some of these repellents may be dangerous to the user and may require a pesticide permit to use) Repellents to repel cats include allyl isothiocyanate (oil of mustard), amyl acetate, anethole, capsaicin, cinnemaldehyde, citral, citronella, citrus oil, eucalyptus oil, geranium oil, lavender oil, lemongrass oil, menthol, methyl nonyl ketone, methyl salicylate, naphthalene, nicotine, paradichlorobenzene and thymol. Oil of mustard, cinnemaldehyde and methyl nonyl ketone have worked in some instances.
Don't bother with ultrasonic devices either. There is no evidence that I am aware of that they work. Also ultrasound is a weak frequency. It dissipates very quickly even if it was annoying to animals assuming they could hear it. I would visit http://icwdm.org/handbook/carnivor/FeralHouseCat.asp it has a link there on how to handle cats. Otherwise, unless you are willing to trap them and possibly suffer legal consequences, there isn't a lot you can do other than fortify your property. There is no magic in this business.
Of course, in the final analysis, trapping may be an option depending on the laws in your state.

Barrier Methods
Fence your garden and or property. You can reduce the climbing of the cats by angling the fence outward away from the garden like this / away from the garden. I would estimate that the fence would need to be wobbly and at least 5 feet high at the peak. If electrical fencing is legal in your area, all the better as it will add to the effectiveness of the fence.
Repellent Methods
Non-Chemical Repellent Systems
?  Motion sensitive sprinkler system (Can only be used during non-freezing weather and cats may become wise to it. I would love to hear from anyone who has had an opportunity to use it)
?  Cat Pad: This device shocks them when they step on it with a low voltage shock. Problem with the device is that the pads are only a few feet square in size.
?  Chemical Repellent Systems
?  Warning: Chemicals may be dangerous to you, the environment and/or your pet(s). Some of these repellents may require a pesticide license to use in your state. You should also be aware that repellents have a spotty record of working as animals only need to walk up wind or past the problem odor. Some times if the need for food is so great, the animal will tolerate the odor to avoid starving.
?  Repellents to repel cats include allyl isothiocyanate (oil of mustard), amyl acetate, anethole, capsaicin,
cinnemaldehyde, citral, citronella, citrus oil, eucalyptus oil, geranium oil, lavender oil, lemongrass oil, menthol, methyl nonyl ketone, methyl salicylate, naphthalene, nicotine, paradichlorobenzene and thymol. Oil of mustard, cinnemaldehyde and methyl nonyl ketone have worked in some instances. from Fitzwater, W. D. 1986 article in Pest Control Magazine.
Trapping Methods
Trapping: remember cats are considered private property in most states. So if you trap and remove someone's cat you can be held liable for property damages not to mention being called a cat murderer. If you want to learn how to catch cats, get my book, the Wildlife Removal Handbook. It has a chapter on trapping cats. You can also learn a lot more about controlling cats at http://icwdm.org/handbook/carnivor/FeralHouseCat.asp   

Cage traps can be very effective on cats as are footholds. since more training is needed when using footholds, I will just talk about cage traps. I guess before I continue, I need to know exactly what you want to happen. If the issue is keeping the cat out of your yard or if the issue is to capture the cat and have it either killed or given to someone else.  If you catch the cat in a cage and then decide to release it, please understand that it will be extremely difficult to catch him again in a cage trap should you need to. It is possible but it can be very hard, even for professionals. So you need to be very clear about what your plans are before you begin trapping.

First, follow all state and local laws before implementing any trapping program. The cat lobby is extremely powerful and vocal. Even if you abide by the law and something happens, be prepared for the fall out.
Second, whenever you begin trapping, be sure to use enough traps. One trap is rarely enough. Wire the doors open (so they can't close) and bait them on a regular basis so the cat becomes familiar with it. Dry cat food would be a good initial choice.  Once you begin to notice the cat eating the food (remember, other animals will eat it as well like skunks (see our page on how to release a skunk before you begin trapping). http://icwdm.org/wildlife/skunk/skunkrelease.asp  
Third, put dirt or grass down on the floor of the traps so that the cat isn't feeling cage beneath his feet.
Fourth, cover the trap with a tarp. Cats like to enter and explore dark places.
fifth, you can try a double door trap like a tomahawk 107. Again cover the trap and put the trap along a trail area.

For more information on trapping cats visit  http://icwdm.org/wildlife/housecat.asp  and http://icwdm.org/handbook/carnivor/FeralHouseCat.asp

there is certainly more to add but I will need more information such as how often the cat visits, could the damage be other animals etc.
Special Situations
?  For scratching, try smearing the item with vaseline so if they put their paws on it they will get greasy. Beware however, that the oil may stain the item you wish to protect. You could also try to screen or cover the affected post. But this may only force the cat to move to another one.
?  

Techniques that probably won't work
?  Ultrasonic devices. There is no evidence that these products are effective.
Disclaimer: As with any activity, remember that animal damage control comes with its own risks and problems which can include but are not limited to legalities, health threats, and personal liabilities. Be sure to follow all state laws governing wildlife and make sure you have a thorough understanding on how to resolve the animal damage complaint. My advice is only as good as your understanding of me and my understanding of your situation. If you have any questions be sure to write back.