It could easily be done with a vending machine. When you pick up your permit you leave $100 (or whatever) deposit on your credit card and get your WAG bag. When you finish your hike you go to the machine at the trail head (or close by) and have your WAG bag barcode read. It then deposits it in a tamper proof bin designed to be easily swapped out and hauled away. Your card is credited back the deposit. You leave your bag somewhere, you lose the deposit.
I’ve read dozens of schemes like this for making people use and remove their wag bags. They are all either totally unworkable or trivial to defeat.
Pay your $100 deposit and then leave the bag in your car. (That’s the smart thing to do; if you lose the bag, you’re out $100.) Climb the mountain and poop wherever you like. Get the bag out of your car and have it scanned. If the machine weighs the bag to make sure you used it, just scoop a little dirt into it, or poop in the bag at the trailhead. Even with a live 24-7 bag inspector (obscenely expensive), there is no way to confirm that the bag contains ALL of your poop from the trip. And what if you did a dayhike or one-nighter, and didn’t take a crap?
