you can totally do this. in a smallish paddock, or a large one even.
you look at it as "catching" your horse. or , really , making your horse come to you in a paddock. once he comes to you, you then turn and walk off. chances are, he will walk along with you.
as you move along, you can send him off and draw him back. That means, you ask him to step away from you, you let him step off a few steps, then you draw him back and walk off in a new direction . it is this drawing, sending redrawing, (a kind of 'dance') that is the essence of "join up".
As to the specifics of that:
you walk toward your horse, and stop a ways off. See if he'll walk toward you . make a little noise to get his attention. if he looks at you with curiousity, good. allow him a little less pressure by turning your "core" away from directily facing him to facing off at an angle. if he just stands there, give a minute or two to think about it, then shuffle the ground with your feet, or swing the lead rope, or , as I do, pick up a little stick and toss it about halfway between the two of you. what you are doing is interrupting him, and asking him to choose a direction, but you are asking him to MOVE. if he chooses away from you, then you walk toward him, and make a bit more of a commotion. you might say, but won't that drive him off? well, yes it will, but it will also make him have an uncomfortable feeling when he turns his back on you and moves AWAY from you. chances are he will run a bit, but he may also leap forward (spook) but then turn to face the thing that scared him. That's when you stand still, turn your core off to the side a bit, and 'invite' him in. he will either
1. come toward you.
2. walk away
3. stand transfixed.
if he comes , you praise him verbally, and make yo9ur body position even more inviting (turn your core off side, exhale and become "passive" in your posture).
if he goes away, as soon as he turns his back to you, make a commotion! he made the wrong choice and you want to make that uncomfortable. scuffle the rground, use the leadline to smack the ground, wiggle it. do whatever it takes for him to react. if he turns to you, go back to inviting, if he runs off, follow him and interrrupt him when he chooose AWAY, and reward him with pressure off when he chooses TOWARD you.
in if he stands transfixed., wait a bit, invite quietly with body posture, add a tiny bit of scuffling, very small things to make him break out of the transifixed state and choose to either approach or run.
That is the basics of catching a horse out in the open. this IS join up. eventually, the horse will come to you with the very smallest of shuffle of the leadrope to get his attention.
Does this explanation make sense? I could show you in just minutes, but in words it is much harder.