The great mouse experiment

I haven't caught a mouse in quite a few weeks, but I did hear one about a month ago one night while watching TV. There was no mistaking the sound. So when I went to check behind the "mouse door" in the guest bedroom upstairs I saw an empty trap amongst the other ones that still had their peanut butter and were still 'unsnapped'. Somehow a little bugger had gotten the food but managed to escape.  I went online to search for more ideas on how to stop this problem.
One YouTube video said to throw a bunch of 'mouse blocks' around the attic. They're poison that attracts the varmints and kills them by de-hydration. After I had done this I read on other chat rooms that this is a bad idea; the mice die from the poison but don't leave the attic and they subsequently smell bad for about 10 days. Great.
So far I've not seen a new one in the set traps, nor have I detected any odors. Fingers crossed that the other tactic I tried might be working, please oh please.
I read that the best way to prevent mice is to block how they're entering the house in the first place.  Supposedly they enter at ground level and the idea is to fill any cracks or holes around the perimeter of the house with expanding foam and/or steel wool. I tried the steel wool last year and it didn't seem to have much affect so this time i tried the expanding foam. I got on my hands and knees, and sometime on my back, like under the bay window, with a can of the very sticky stuff and applied it in as many places as I could find around the front and sides of the house. It's not a very attractive look. The stuff hangs down in blobs and it's an ugly creamy yellow color. A future project of mine is to camouflage it with some gray/brown paint.
The last idea I'm going to try is buying a black light flashlight. I read that if you shine it around the house at night you can see the urine trails the mice leave behind, they're an indicator of where they're getting in. If this works, I will fill in those places with more expanding foam.
With Fall coming I went to get a jump on these critters and outsmart them once and for all. Stay tuned for a progress report.
Here are several pics of the foam in all it's unattractive glory: