Thumbtacks on the ground, piles of sticks and rocks and wire between trees are just some of the acts of sabotage Illawarra mountain bike riders have to avoid.
On Saturday, mountain bike enthusiast and Coniston resident Keiran Volk was riding on a Bulli track when he met up with friends who had thumbtacks punched into their tyres on a nearby trail.
"This is the first time I have come across thumbtacks," he said.
"I started riding when I was 14 and now I'm 28 and I have seen various amounts of trail vandalism and sabotage on different tracks.
"At a track in Tarrawanna I was riding at high speed coming over a blind crest and there was a drop onto a dirt ramp.
"On the ramp, someone had piled up sticks and stuck some so they pointed out.
"I had to make a split decision to pull up and jump over the sticks. Whether someone wanted to injure or kill a rider, there was malicious intent there.
"People can die if their crash riding their mountain bike.
"When there are objects on the track, the risk for injury is so much higher because riders aren't expecting it."
Mr Volk said the thumbtacks could hurt other bush users such as walkers or dogs.
"If we get a flat tyre it is not a huge deal, more of an inconvenience," he said. "But a dog could get them in their paws."
Mr Volk said the sabotage and vandalism showed the attitude people had towards mountain bike riders who were just trying to enjoy themselves out in nature.
Mountain biking is illegal, but commonly done, on the Illawarra escarpment. The state government is proposing to formalise trails.
The plan outlines a network of 82 kilometres of trails on Mount Keira, Mount Kembla and Balgownie, which will be delivered over three stages.
However, there are groups and members of the community who object to the formalisation of the tracks.
Fellow mountain bike rider and Bulli resident Jerry Harriman supports the legalisation of the trail network and hopes, with more education, the vandalism will stop.
"My guess would be people are doing the sabotage because they think they are policing the trails," he said.
"Formalising the trails and more education would help. If we are allowed to be there then hopefully people won't try to hurts us."
Mr Volk believes the escarpment bush should be used as a recreational area because he fears it will otherwise be developed into houses.
"We live in a nice place, it is a great escarpment, why should we not utlise it?" he said.
Mr Volk said mountain biking was like any other sport and needed formal tracks, like soccer clubs had fields to play on.
Mr Harriman does maintenance work along the Bulli trails, including organising rubbish clean ups a couple of times a year, and has regularly come across acts of sabotage.
He also found about 100 thumbtacks semi-buried in leaves on a different Bulli track on Saturday.
"I find logs deliberately placed across the track, I see rocks piled up and broken glass on the ground and there has been wire tied across the track," he said.
"One time a 16-year-old rider was coming over a jump and a log had been dragged and placed on the other side to cause harm.
"The kid came off the bike and got a concussion and cuts."
The men could not understand why people would deliberately try to hurt riders and urged the vandals to stop because a rider could get seriously injured or killed.