When a horse is tied to a tie rail with too much slack, he can step over the lead line and the pressure will cause him to pull back and break something. Or if he is tied too closely to the rail, that can be a problem too. It's also a problem when someone ties the horse to a rail or fence using both reins with the horse carrying the bit. In cases like these, the horse is able to pull down fence panels or bang their teeth on the bits by pulling back.

The best way to knot a lead line is with a quick release so that you can easily untie your horse. If you need to tie a bridled horse to a rail, then you should consider using a separate rope like a “get down” rope. If you are riding with mecate reins then you have that extra eight feet of rope to tie with.

This video shows a simple knot to use when tying a horse to a tie rail.