It's tempting to tie your horse to a hitch with his reins during quick breaks, but no matter what, this isn't a safe move. If your rein-tied horse pulls back, he can easily injure his sensitive mouth tissues, or worse. He'll also likely break the reins.
For tying safety, outfit your horse with a halter beneath his bridle, then pack a lead rope in your saddlebag. During breaks, snap the lead rope to the halter and use the rope to tie. Then use this safety-knot tying method, which will come untied with one pull on the lead-rope end, should your horse pull back.
Step 1. Wrap the loose end of the lead rope once around a hitching post or sturdy tree. Allow enough slack for your horse to comfortably move his head, but not so much that he could catch a leg in the rope.
Step 2. Fold a section of the loose rope close to the post, then wrap this fold around the post and existing wrap to form a loop.
Step 3. Pull the fold through the middle of your newly formed loop, and tighten.
Step 4. Loop the remaining rope up through the folded section to contain it.
Step 5. To release, pull the rope end until all the loops come undone.
Step 6. Remove and stash the lead rope before you remount. A dangling rope can get caught on low limbs and brush, and wrap around your horse's legs, which can lead to injury.
