HOUSTON, Texas (KTRK) -- Deep in the Memorial Park bike trails, avid cyclist Marc Sierra has come across some unusual items."I see a lot of underwear, all over the place, dirty underwear, I also see some unusual men's shoes," he says, before ticking off a few more items of clothing he often sees strewn about.Frequent cyclists know the reality: not everyone uses Memorial Park for routine exercise. Public sex and masturbation in the woods have been an ongoing problem for years. So far this year, Houston Police have arrested five, and charged three men around the Picnic Loop for indecent exposure. Thomas Boozer was arrested in February, Christopher Toomey in March, and Jose Escobar in May."I think it's really stupid for them to be doing something like that," said Rene Gomez, who rides his mountain bike three or four times a week at the park. "This is a public place, you know, like kids are around here, if you're going to do something like that, do it at your house."The most eye-brow raising arrest is Toomey, because this isn't his first time. Four years ago, Toomey was among seven men caught during a Memorial Park sting for the exact same alleged crime. At the time, Toomey worked as a Harris County jailer. He ended up being sentenced to 10 days in that same jail.Houston Police detectives say most of the sexual activities tend to happen during the day, often during the lunch hour. Observant cyclists admit, their eyebrows rise whenever they see someone, not in workout clothes."They don't look like they have hiking outfits on, they definitely don't have bikes or dogs, so you're wondering what are they doing back here," says Sierra.The incidents are not new, and the Houston Parks Department referred all questions to HPD, citing the fact these are security issues. HPD says it does regularly patrol the area, though since most illegal activity take place deep in the woods, it's not often readily visible.The bigger issue at Memorial Park this year, however, are car break ins. HPD says there's been enough recent car break-ins at the park, that members of the Mounted Patrol have increased presence in the area.