Thanks for the input guys. About the garter snakes, I've got a common neonate garter right now, had him for about 2 years, and I've never seen him active during the daytime, he just stays in his hide and only pops his head out to snag a fish or mouse from me when i'm offering. Maybe garters get more confident when they get older?
Maybe I'll try to keep a green snake again. I bought a smooth green snake from petco a while ago, it was weak from the time I bought it, and it's condition just deteriorated till it eventually died. Are both smooth and rough green snakes diurnal? I've heard rough green snakes are more hardy and take to captivity better...