This is a real problem near my home....just half a kilometer away is a motorcycle club, and some of the smaller-brained members can't resist riding their motorcycles on the bike trail that runs nearby.
I carry a cheapo digital camera on my rides....usually to take pix of interesting things I see...but nothing gets a moron on a motorbike off the trail faster that having his picture taken. Works every time.
~Sherry
All vintage, all the time.
Falcon Black Diamond
Gitane Tour de France
Kuwahara Sierra Grande MTB
Bianchi Super Grizzly MTB