Ooops! Nevermind.... I just found it!!!

Now that the lights are out... there it is just crawling along the bottom like it should, right by the big rock.
WHEW!!

OK, now I feel EXTRA-stupid, but at least my snail is safe.
I'm taping over the hole in back with aluminum foil & masking tape for now anyway to be safe. Ack!!
~scared myself~

Better ways to seal up holes for escaping-types-of-critters would still be helpful.... thanks!

Linda