I saw a LOT of gum walls this summer, and most of them were indeed mosaics of gum. Add the heat, and at SFoG the bees, and you've got a not so pleasing situation.
As for SFA, the vandals started those scratches on the S:ROS walls on OPENING WEEKEND! That floored me that people would wait for a brand new coaster and already start defacing it.
As for confiscating gum, you'd have to take away pens & markers too, if you really wanted to combat park vandalism. I think if people were more vocal about their displeasure at others for doing this, things could change. Also, carefully placed video cameras (dummy ones even) with signage that says "you are being watched" would greatly diminish the vandalism.
The final thing is for park officials to look at their high vandalism areas and re-think their queues, etc. IOA had a terrible grafitti problem in the first few months, but their team kept changing things so that it became harder and harder to do.
It's sad that this has to happen at all, but not everybody has the "love" for these places that we do.
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"You have to scale a lot of lift hills to coast easily..."
Jason