To deal with thieves / snatchers, use lots of chained dogs at the entrance ways. I do not think any got by my dogs once I had 4 dogs to protect each entrance.
As for trouble makers and the guard... I am not sure how needed guards are, but there is a side effect that can make demanding nobles punishments a good thing.
The first thing to do is keep "The Hammerer" under lock and key so he can't kill or maim any dwarf. Then have a few guards but no jails or cells. If a dwarf gets a punishment and there is no way to punish him, the sentence will be commuted and he will get a happy thought at having a reduced sentence. I am not sure if a guard will ever kill a dwarf as a punishment for a crime (beyond a dwarf going berserk) where as "The Hammerer" definitely will wax more then a few dwarfs.
On the other hand, the nobles will go insane after a while if all their request are ignored, so they will either die or be killed at some point unless you keep them 'safe'.
For example, a countess at my fort was constantly pissed off by the dungeon master and finally went insane. It was her top thought all the time. You see, the dungeon master was really useful and never made any demands so I gave him a sweet room and a kick ass tomb. The countess was really angry that a 'lesser' had a better tomb then her (she, in fact, had no tomb). She started making a bunch of demands that were never addressed, and there was no jail to punish anyone. The count-consort was also starting to wig out too.
Eventually the countess went melancholy and killed her self, and the count consort went nuts and was whacked.