Trailer brake problems

Need some help. I've got a one year old tandem axle aluminum trailer, made out of state, that won't back up all the time. It backs fine on smooth surfaces like boat ramps, but when I hit any rough spot or back for more than 35 feet, the brakes lock up. By rough I mean an easy gravel drive or concrete to grass transition. Its making me crazy. I don't have alot of time to trouble shoot as there isn't enough daylight as it is, to get important things take care of. Any ideas as to a cause and fix, or someone in west or nw houston to take it to?-Tom