On newer trailers, especially with disc brakes, there is a look out that is/can be installed in the brake line to keep the brakes from actuating while backing, it is tied into the reverse light circuit. The biggest problem with surge brakes, the trailer has to be towed level for the best results. Trailer nose high, the brake action can be delayed and weak to not at all. Nose low, the brakes will activate prematurely and tend to slam brake. I have built, serviced, and towed many trailers with surge brakes. For the novice that tows every once in awhile, they are great.