I spent 8 years using a Tarptent Notch, and the last 2 with a MLD Solomid XL, as "tarps" that I leave one or both doors open on when the weather's good. Also use a ZPacks Hexamid Pocket Tarp that has no doors.
I've never had anything except a persistent scorpion that ended up getting squished come under my tarp that I know of until last month, and that was a lot bigger than a raccoon or possum.
Black bear, hog, whatever, it woke me up breathing heavily into my nose and mouth, the only things not covered by my sleeping bag. Guess that'll teach me to use a bag when I've got 3 quilts...
Yelling "Get out of here!" at the top of your lungs and blindly thrashing around apparently works wonders for getting rid of unwanted visitors, so I guess I can recommend that, at least until I'm able to give feedback on the quilts with built-in holsters and portable electric fence that I'm shopping for