This is the title of an interesting peice from singletracks.com:
http://www.singletracks.com/blog/trail-advocacy/illegal-trail-builders-r...
The writer says, "...renegade mountain bikers had secretly cut up to 30 miles of trails... Despite having 255 miles of trail access in national forests around Tahoe, that isn’t enough for the free-riders."
These guys overseas have 255 miles (410km) of local trails, and I'd assume much of this would be dedicated to MTB. Looking at our own back yard, we have 187km of trails (this includes some, known illegal trails) and only the recent action at Manly Dam makes around 2km of them dedicated for MTB riding.
The writer goes on, "On the spectrum of things that are bad for the reputation of our sport, building illegal trails has to be one of the worst (if not the worst) things we can do. So if you’re thinking about putting a shovel to dirt this spring on land you don’t own or have permission to use, give us all a break and volunteer with your local club to improve existing trails."
You have to agree with this and that the only way forward is by doing things the legal way. It's a nice idea to channel energy into clubs, but the issue here is that our local clubs don't have the authority to maintain trails so in reality there is no outlet for those wanting to do the right thing.
So while I completely agree that illegal building is damaging, local authorities need to look overseas and realise that in order to prevent it they must engage local riders. What this also shows is that no matter what utopian trail network that exists, sadly there will always be a rogue element (100% compliance is an unrealistic goal), but that the majority of riders will pitch in to undo any damage rogues may do given the chance.