Question
We are putting in landscaping for our new home and want to use river rock rather than mulch.  How deep should the river rock be?  Is there an industry standard or guideline on this?  

Appreciate any help or guidance you may be able to provide!

Answer
make sure you use a geotextile(weed mat) under it. and you will have to do weed pulling and herbicide spraying periodically because weed seed will sprout amongst the rock eventually.
depth of rock depends on how big the rocks are. usually 2" is enough if it will cover the geotextile completely.