Not all horses are slow off the leg. Others are too quick. In this situation it’s your arms not your legs that need the break. Your horse can only pull if he has something to pull against so you need to teach him that there are other ways of stopping.
So much is written about your lower leg but how often do you read about your upper leg? Pushed into the saddle your knee and thigh restrict the muscles that work the shoulder, automatically slowing your horse down. This means you depend less on your reins.
Warm up and try this exercise.
Start in walk. Choose a marker to make a transition to halt. Think of your thighs and knees as a clothes peg and squeeze into your horse as hard as you can.
At first you might find he’s a bit confused by your change of style. He’ll slow down but may not be sure whether to stop. Use your reins initially just to make it clear. When he halts be quick to praise him. It’s too easy to forget and only criticise.
Walk and halt until you can stop with just the pressure from your knee and thigh. Don’t release the pressure until you want to move on. This works on all horses and results can be instant. If you have no reaction you just need to squeeze harder.
Once you’ve mastered walk to halt try trot to walk and canter to trot. Release the pressure the second you feel the new pace. It takes some practice to be able to create smooth transitions but when you’ve really got the hang of it you can try direct transitions from trot to halt or canter to walk. Just squeeze with your upper leg until you reach the pace that you want.
Practice until it becomes second nature. Every time you want to slow down use your knee before your hand. Your horse’s mouth will appreciate it and so will your arms. In time you’ll be able to collect and lengthen just by changing the pressure from your knee but that’s something to think about another day.