
I find it often starts as a lazy habit when the pups reach a stage where our walking speed is too slow for them to trot, but faster than their walk.
I did as on poster said trained the trot in my persistent pacer. Generally you need to give a little lift at the start, and move off fast. some can pace at speed, so with these you start and if they go wrong you stop go back to the start and say trot and move them at the correct movement from the start.
Another explanation of pacing is imagine a pantomime horse where both people move the leg on the same side forward together. In a proper trot the legs on each side come together in the middle and apart like scissors, as opposed to follow the leg in front.