Just keep the yard cut and get rid of any brush piles.
Garter snakes ain't looking for people to snuggle up to.
I don't really understand the urge to get rid of them though, it's not like they are any kind of danger at all.
In fact they are quite useful, unless of course you would like to replace them with the pests they remove.
The last house I lived in had a sump that ran out to a drainage easment, it allowed things to get in. Things like silverfish and I guess one anole type lizard.
My ex saw it first and freaked right the heck out. She demanded that I crush the life out of it.
I tried to catch it...never did, I did see it once though.
Metalic blue, very handsome.
I guess they are kinda smelly if you pick them up, garters that is.