Horses hanging head over gate to be haltered/unhaltered can get someone hurt, if they aren't used to it. And not pleasant to have finger caught in halter and drug over gate if horse rushes off. The poster that wrote this, is used to doing it that way, but it is not something I would recommend to someone that is not experienced.
Are you talking about a real harness, or a halter?
If halter? Take horse through gate, and walk in maybe 10 or more steps, and turn horse to face you, with your back to the gate, make the horse back up several steps. Then you can either have horse back up a few more as you are releasing halter, AND stepping back yourself. Horse backing up and you too, means there is space between you if and when he wheels and takes off, possibly kicking out as he does.
And never, but never, stand at gate and shout HAH at horses while waving your arms at them, or the halter and lead as that teaches them to take off acting like the village idiot.
Horses make me a better person.