Be sure to use a 6 point socket, that way you lessen the chance you will round the bolt head off.
Also what I usually do is use a hammer and smack the breaker bar to help bust the bolt loose. The "jarring" seems to loosen it up easier than using a cheater bar.
Are you trying to take the slide pin bolts out, or the caliper mounting bracket bolts out (12mm vs. 17mm socket, IIRC)? If you are trying to take the slide pin bolts out, I'm surprised you having twisted them off yet, they are small bolts and are only supposed to be torqued to somewhere around 20 ft. lbs. Now if you are trying to take the caliper mounting bracket bolts out, then I could see where you are having a problem....they are bigger bolts, usually rusted, and are torqued somewhere around 60 ft. lbs, IIRC.
BTW, I always take the caliper mounting bracket bolts out, instead of the slide pin bolts, when doing brake work. Just my preference.