It's something of a catch 22, really...if you put the bull snap on the horse and the panic snap on the trailer, if the horse pannics and you undo the panic snap that big heavy snap is clonking your horse. If you do it the other way, you have to get too close to your panicing horse to undo the snap.
But, there IS as way to do it properly, but it takes some forethought. You will need a bull snap with a short loop of cotton lead on it large enough for the panic snap to pass through it easily (or a rope halter with a large tie loop), and a double lengthe trailer tie (or a regular length lead rope with a panic snap) Tie or clip the bull snap to the trailer, and pass the emergency snap through the loop and bring it back to the tie ring in the trailer.
Now if the horse panics, you can undo the panic snap and let it free, and theres no big heavy trailer tie with a panic snap clonking him and making him more scared - and he has a safely short handle dangleing from his chin
