Over the fence and into the neighbors' yard has always worked well for me.

In all seriousness, I generally spill the bowl in a part of my property where there's only mud and flagstones. Over the 8 years I've lived there, there's been no ill effect that I can tell. Nothing ever grew there in the first place and there's been no build-up of gunk/grease, weird smells or animal activity. I do try to make sure that the bowl is pretty full of water before dumping, just so whatever else is in there is more diluted.
=R=
By protecting others, you save yourself. If you only think of yourself, you'll only destroy yourself. --Kambei Shimada
Every human interaction is an opportunity for disappointment --RS
There's a horse loose in a hospital --JM
That don't impress me much --Shania Twain