Question
The wild cats in the neighborhood are using my vegetable garden box as a liter box.  Is the urine and waste toxic? Will it harm us to eat the vegetables grown there? What can I do?

Answer
The main concern is coming in contact with the feces that may (probably) contain worms.  The pH is lowered by the urine which over time would have to be corrected.  Your above ground crops are fine to eat.  Root crops should be thoroughly cleaned and cooked.  
I'd fence the garden to keep them out.  Bird or deer netting is cheap and will work well.  Jim