fearsome

I feel you you guys and know exactly how it feels.

The way we solved the problem was to put up a fence around the track and padlock it....it ensured that only active club members had access. Tho i feel that this may not be a option for you guys yet. You could propose it to the council with all said reasons and also offer to take the cost of the fence. Worth a try....

If the fence is not an option you could use large metal poles and lay then across the track on the staight or corners and paddlock them down (kinda like a boomgate but laying flat on the track) you'll need to maybe dig a hole in the side of the track and place an anker type thing to padlock the poles down.

This will cuz hassle to the guy running on it. They have to slow down and navigate around it. If you put it in the corner where the damage is normally done then thay have to slow down there navigate around it hence the track doesnt get damaged.
or they dont like it and piss off
I dont think it would be too expensive and you could place them in strategic places around the track.