LOL...20 lb cat...holy. Is it half bobcat?
Ya, I'll try not to dress up as a snake if I come visit.
That windows screen would probably work as long as it's deep enough in the ground and high enough they can't get over it. I know nothing about snakes except what I've read so you'd know better then me. We have terrorist snow flakes in the winter though...man you gotta dodge those suckers.
I was going to suggest putting down some kind of mulch on top of the whole strip of area you don't want growing...but A) that looks like a huge strip...and B) if it's not in your yard why spend money on mulch. Although even if you spray it, it will probably come back after a while. Hey, if you had a wood chipper you could chop down some of that stuff behind your house and make your own mulch.