Years ago I sealed up all the entrances to the crawlspace, but last week
I noticed that one had come off. Argh! I wasn't about to just seal it
back up because I figured that with the cold weather coming on
(Berkeley, CA, not freezing, but quite chilly in the winter), some
animal was probably under the house.

I figure before I seal up (this time with a door and latch), I have to
get whatever animals out of there. I started by putting some strained
dirt over the ground just below the ~18x24" opening, smoothing it
carefully to reveal any footprints of an animal going in or out. Next
day, sure enough, footprints, maybe about the size of a small cat (but I
figure it wouldn't be a cat, but who knows?).

I tried a trick I'd heard of and put an open container with some rocks
in it (to keep it from tipping over) with ammonia and a rag, to disperse
noxious and offensive fumes, right in back of the opening, so the
animal(s) would have to pass the concentrated fumes when going in/out. I
figured that after a day or two the animal(s) would find friendlier
accommodations. After two or so days of this, footprints are still in
evidence.

What can I try to expell the varmint(s)? I figure I can maybe work up a
one way door of some kind, but it seems tricky.

Dan