I plow rein, I open my hands wide, where his eyes can see them, and encourage him forward with my body movements (leaning forward for forward motion) squeezing or kicking his sides, and kissing, all indications we are going FORWARD. The moment he takes one step forward, "OH GOOD BOY!!" then when he backs again or stops, IMMEDIATELY go back to the forward movement signals. If he's throwing his hips or head to one side or the other when backing, my wide oepn hands go into motion, tipping his nose INTO the DIRECTION i want to go, he sees my hand in his peripheral vision, which "closes the door" to that side. This is strictly for backing up.
Stopping and bulking is are totally different response.