I've only searched for ones in wooded areas, but it's interesting to know that people hide them in places like that (fake electrical outlet).
I tend to not try and stick my hand in places that I can't see into, such as trees. Sure the cache may be in there, but so might other stuff and that's not cool since I sometimes go looking alone. I'm also not a big fan of moving old and rusty metal objects. I don't bring a backpack full of supplies or anything so I never have gloves or anything.
I'm kind of interested in some of these urban caches though, I'll have to look for a few.