It's counterintuitive, in a way, but basically, when you approach the horse, out in the pasture or paddock, if they turn away from you and walk off, you make a little bit of a commotion. This puts a bit of pressure on them and makes that choice they made, to leavey you, feel uncomfortable.
They will usually jump a bit, stop and turn around to look at you like, "What the heck????!!"
When they do, you pause. Don't come closer, just stand with your body facing cocked off at an easy, relaxed position, not staring hard at them. you are becoming 'inviting' to them. if the come toward you, you can even back away a little to further invite them.
If they say, "oh, it's only her. I'm not interested", and they turn away from you and walk off, you repeat the small commotion (that means things like slapping your thigh with the rope, smacking the ground with the rope, kicking some sand. you aren't really driving them directly so much as making enough noise or activity to make them turn, stop and look and rethink . Then you offer the calm/inviting stance and wait for them to choose again; you or away.
If they walk off, you follow a bit, and make that interrupting commotion, stop and wait when THEY stop and wait. They will eventually realize that things are quiet when they stay looking at you, and difficult when they don't , and they'll allow you to approach without changing their mind and leaving. If they do, you know what to do!!
I highly recommend this. I started with treats (but my horse wasn't testing me, he was terrified of us) and soothing talk, got him to trust me first, began weaning him off the treats and only rewarding with praise and physical affection. Keep in mind, this was just to get him to the point he wasn't afraid of me. Your horse isn't afraid of you, it doesn't sound like.
Trigger is to the point he USUALLY comes at a trot when he sees me, but from time to time he tries to 'flirt' and prance around and run wide swinging arcs around me... neener neener! Can't catch me!
When he does that, I throw my arms up (I usually have a catch rope or a heeling rope these days, no halter and lead needed), stomp at him, SSSHHHH or HA! (as in GO then, FINE. I didn't want you anyway) and he will almost always stop acting a fool, immediately turn and give me both eyes and come to me. He seems to think: WHOA! Hang on here! Wait just a darn minute! HEY LADY. That's not how... no no no... nooo, you're supposed to chase ME not drive me away!
He was the untouchable, uncatchable horse in April of this year. Now I can't run him off, he just can't stand it - but it took almost 6 months of almost daily interaction to get him 'easy to catch'.
Be prepared to be patient - but also be the top b#*$*h in his pasture (That doesn't mean be the meanest or an abustive *(&(^%$% in his pasture btw or you could create an entirely different sort of monster), in his life, and right now, it sounds like he doesn't think that's you.
You mentioned your other gelding was never like this... well.
That's your other gelding.
THIS gelding IS like this. (we have 6 horses and each one is as different as a fingerprint - each and every one of them rides different, has different spooks, different personalities, they are individuals, just like we are).
He's not being a bad horse mind you - he's just testing the herd dynamics, which is perfectly normal. That's what horses do - they constantly test one another to see who's the high horse. If he thinks he's got his bluff in on you, you're going to be in a world of hurt if you don't change the dynamics and quickly.