Yeah, I've been almost bit by a police dog once. My girlfriend and I went for a walk in the park in St. Petersburg, RU. It is a former Royal Park with antique marble statues in it, and what not. So it closes for the night, and has only 2 entrances (it's free to visit). We walked up to one of wrought iron entrance gates only to find them closed. Since it wasn't anywhere near closing time, and we could see people inside, I thought the gates were closed for maintenance. Walking around the whole park to find another entrance would take at least half hour or so, so we decided to jump a granite embankment on the park edge where it borders with a water canal.
As I was hopping over, I saw a German shepherd tied to a tree, barking at me. I figured, probably some dog owner left the dog here for a minute. Not giving this a second thought, I hopped over and gave my gf a hand. As I was turning around, I came within the reach of a dog, and it launched at me and grabbed me by the arm. Luckily I had a jacket with loose sleeves, and the dogs teeth snapped the cloth, not my arm.
I wriggled myself out, and we left. About 10 minutes later as we were walking in the park, I saw police officers with this very dog patrolling the park...