Mice can, and do, squeeze through much smaller holes than you would think possible. You can put poisoned baits in your shed and kill them when they ingest those baits (just be sure other, more desireable critters cannot get to the bait), you can place those spring traps to kill any atracted to the bait placed on that trap, or you could try hanging a dryer fabric sheet (or two) in the shed. I was told last year that this would keep squirrels out of my shed and it did, but for those of us with some types of Asthma those sheets can also keep us out.

Thansk for the ideas. I've been considering mothballs as well.

I checked today and my traps (baited with peanutbutter) we untouched! Progress!!

Keep in mind that the active ingrediant in moth balls is a class 1 carcinogen and that Federal Law prohibits the use of moth balls except in tightly closed containers. No one in their right mind would put moth balls where anyone would be exposed to a potential carcinogen.

Kimmsr:
I am aware of the risks associated with mothballs. I was thinking that exposure would be at/near zero if I put the mothballs in a porous container in a remote corner of my shed. No one goes in the shed except me and that's for a brief moment once a week or so to grab something or back out the tractor. I definitely wouldn't use them in my home, where possible contact (physically or in the air) would be considerably higher.

Still looking into this solution however. Thanks for your input!

I have been finding mice in my "chipmunk swimming pool". Check out the 'getting rid of chipmunk" thread. With the grate across the top of the pool, squirrels, birds, dogs, are kept out while chipmunks and mice can get in. No poisons, no chemicals.
Kris

Last year was my first year in our new home which is next to a greenbelt. My dream home. I put out bird feeders and had Goldfinch and all types of birds and hummingbirds as well. Then I had Chipmunks and Squirrels. I was happy. The neighbor warned me that I would also have RATS. One night I turned on the patio light. There was some type of rodent shaking the beejeebers out of a Suet feeder that was hanging in my Laceleaf Maple tree. I was excited as I thought it was some cool animal from the forest. I got my book and was able to identify the rodent...a large NORWAY RAT. Then one night we had about 5 running through the yard. Freaked my husband out. We called the exterminator. We put out bait stations. They are enclosed so cats and dogs don't get in there. Still, you run the risk of a animal eating the sick rodent. We have no neighborhood outdoor cats. The bait stations did the trick and we had rat traps under our house and it turns out we did have a few rats under there. They can eat wires and really cause problems. I would either get bait stations or keep trapping them. Remember for everyone you see, there are 50 more. A master-gardener told me that.