depends where you live really.
And I think most people get caught because they either tell a semi-buddy in a bar after 6 beers, they let emotion guide them and they toss the body where a jogger will find it the next AM, or they are stupid enough to wear their cell phone when dumping the body.
I mean, if your woman goes missing, and you have an unusual, unexplainable trip to the Florida Everglades on your cell pings that same night, your ass better get a lawyer.