The best way to prevent this is a tip I was told many moons ago. You should think of the give and retake of the rein in three stages which should happen over three strides. The give, the stay and the retake. The stay is important but also missed, it allows the judge to clearly see that (hopefully!) your horse does not change it’s frame or alter its’ rhythm when the contact is released.
This photo shows a good although slightly exaggerated give and retake. The rider is showing a clear ‘Give’ and the horse is maintaining its outline and balance that is what the judge wants to see.
Another thing to be wary of is how you give the reins, a lot of riders will reach up the neck but never actually release the contact, this will not fool a judge! As per the above photo the judge wants to see a clear loop in both reins.
Don’t forget this Tip Of The day for teaching a horse about Give and Retakes as well.