Sorry this has taken so long to respond, but I've been away on business.

If your body fat is WAY down - like under 10% (be honest!) yet your butt is more bublicious than you'd like then it is probably genetic. (remember a bubblicious butt is to be revered - unless you are a top. First of all, if you are trying to build muscle, don't do cardio; You'll ruin your progress. Forget "spot" reducing - its a myth. Try going on a "contest" diet, and really get the bodyfat level down. Your ass should finally go down with it. Doing squats will, make it look bigger at this point. You might try a cutting or ripping gel on it - along with a strict diet. (I have not had good success with them - but others say they have.) I do know someone who had their behind sucked (lipo not rimmed) but that is sort of drastic.

If your ass is too wide - that is genetic too. Look in a mirror. Are your hips too wide? If so, your booty will follow. Again diet will help to a point. If this is the case, try to camoflague the problem by doing exercises to thicken the waist (obliques). Side bends with a dumbell rr twists on a resistence machine will help. A wide waist is bad if you tend to compete, but a small waist and big hips on a guy is probably worse. Also work your lats to provide a bigger taper. Wide lats, combined with bulging obliques will take away from the horizontal heine. This, combined with squats or "butt blaster" work should provide a shapely dereiere that everyone will want to get into.