I think Jenny's idea is great! I also think it would change little, but if it makes any difference, it's still worthwhile.
Education is key. Unfortunately it's not enough.
Enforcement is what can really change things. Unfortunately enforcement is generally not well funded. The Park I volunteered for last summer was one of the busiest and most profitable in CO (Chatfield Res). Unfortunately while we watched as thousands of cars and boaters paid their entrance fees, the Rangers were low on fuel and budget, and that was impacting their ability to do what they planned.
So PAYING for enforcement is a big factor, and few are interested in doing so. IMO, legalize drugs, tax them, and take those billions of dollars and spend them on things that work!