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Go steady if you ride New Biggin Plantation/ Tankersly / Chapeltown area, the last few days have seen various hazards built on the relatively blind dips and landing areas of some trails. It's not done to block the trail or stop people using it, it's simply an attempt to cause harm to someone. I've cleared all that I came across this morning but I'd done the same 2 days ago and various others have appeared since.
Do you have bigger images?
Report to the police. Even if their cheeky trails.
I'd consider getting a wildlife cam too - they can be easily hidden.
Bigger image attempt:
As suggested, I've messaged SY Police to see what they advise.