You can also take a wrench with you, to quickly remove the locking wheel from your cart. Maybe replace it with a non-locking wheel from another cart.

Shouldn't be difficult to find carts left near or beyond the edge of the parking lot.

I find the locking wheels annoying, because they're so often defective and make it a noisy struggle to get your cart through the store. But years ago I also had a neighbor in my apartment complex who would walk home with a cart every week, and would just leave (a dozen of) them there... she couldn't be bothered to push the empty carts back to the store, not even once. I'd think a $1 deposit/return system for carts would work better, and give the homeless in the area some gainful employment.