So I found this glitch by accident. So here's what you have to do.
1. Have any cops chase you to a ocean.
2. Find the area near a sewer or docking station where the land has a dipping spot.
3. When a cop chases you swim away. So the cops loses there focus on you. This will result in the cops to start trying run up the hill. But , ending up soft locking them trying to get up.
4. Kill a cop an repeat step 3 over and over. This will result in a hoard of cops unable to do anything. Some cops may rotate and point there gun at you but, they wont shoot you.
Some cops may break the bug but, enjoy the massacre of mayhem you will cause :)

This works on the xbox 360 and pc release of Saint Rows 2 (and maybe 3)