I believe the SS don't have to be on their backs 100% of the time. When the Bush twins were caught drinking underage at Chuy's, I think the SS agents were actually outside the restaurant, not inside with them.
Also, I'm sure there is some sort of panic button available for these situations, where if something WERE to go wrong, the person under surveillance would be able to alert the SS. Think about it, if someone's under SS surveillance, the agents aren't going to be in the bedroom while they're having sex, or watching them while they shower. There are a whole slew of situations where a person would need or want to be separated from the SS agents, I'm sure they know how to handle it.
The President, obviously, would be different, but I doubt there will be a President in office AIing into anything soon.
