Aw, what the heck? I know a lady who has a big birdfeeding setup outside her house. It is patronized by vast number of birds, a few squirrels, and one rat. The rat has been coming there for years now. He has harmed nothing and hurt no one.

One rat outside is not a problem. If you get many rats and they come inside your house, that can be a problem, but one rat in your garden is not a problem at all as far as I can see. He's just a small rodent, for heaven's sake, and he's looking for food same as any other small rodent does. If he's not in your house, what's the problem?

Ever seen the movie "Ratatouille"? ;-) You might feel kindlier toward rats if you did.