I strongly advice anyone who has horses with shoes on their back feet to always take the halter off, no matter what.

I used to work at a stable for many years and the owner lost two horses because of this. You know how sometimes a horse will scratch his head with his back foot almost like a dog? Well, her horses occasionally do this, and the shoe on the back foot was too long and the halter accidentally became trapped between the horses hoof and shoe in the night, inevidably pushing against the horses brain stem eventually killing it. Even if your horses halter is a perfect fit, if he has shoes on, I'd advice against it.

Although I know how hard some horses can be to catch so I definitely know why people leave the halters on.