I understand your perspective. I agree with some of what others posters have said. Consistency and fairness are important as are clear boundaries.
However, as much as one sometimes sees a too softly softly approach all too often one also sees the overpowering, overly domineering, always getting after the horse approach too, which is just as dangerous and damaging. These horses lose their personality, and their ability to express themselves such that they often channel this frustration into other areas.
I see these overly restricted horses all the time. Sure they maybe 'safe' but they are also insensitive, dull, and stressed (internalized). They are the same horses that suddenly take to aggression towards the other horses, get stomach ulcers, start cribbing and weaving, the list goes on. Nobody listens and nobody cares.
There are many reasons why a horse can deomonstrate 'aggression' many of which are not sight dominance. To label it all as dominance is to overly simplify the capacity of every horse. Much the same as with dogs, aggression can be dominance, but it can also be many other triggers including insecurity. If your horse in insecure then dominating in such an aggressive manner will not help it in the best way. It needs clarity, clear, balanced, emotionally neutral, OBJECTIVE leadership. This is why I personally do not use any raised voices around horses. As humans it usually brings emotions into our action, whether real or perceived. Equally it tends to become a crutch for us and allows us to focus less on our actual body language.
Anyway in terms of your horse and the field. Personally I only carry a rope. That's all I need, but I always carry it. Mine is usually 20 or so feet long and will have a hoop on the end with a carabiner. With a couple of loops knotted at two points it serves a wide variety of purposes.
However in this case I would be using it to control the horse and create a barrier. This is how I would do it. I do not know where you are in terms of your ground skills or confidence, so please do not take any risks you are not sure of, this is simply what comes to me.
There are a number of ways to dominate the horse in a more neutral and less physical way depending on the personality of the horse. One way is to use a feed bucket, but I suspect that is not right for this horse. Initially I would simply spend time in the field. Only allow him in to you when you invite him. At first don't allow him at all. When he approaches raise your posture, be absolutely solid in your mind and take a step towards him then stop dead and bring the rope up across you like a bar in a snapping fashion. If he stops then great. Stand absolutely still yourself. Relax your arms but do not fidget.
If he moves take an abrupt, part step and raise the rope again.
A horse like this needs to stay out there away from you for some time. I've stood for as long as 10minutes before I've invited them in.
If he does not want to stop when he is approaching you then whirl the rope (aiming in the direction of his shoulder) point away and step in towards the shoulder. In others Words send him away.
All of this is totally neutral. No aggression, no anger, no fear. Entirely neutral. You cannot believe the power that very fact has over a horse. Especially when 99% of their experience of humans has been emotionally fueled.
Secondly a horse like this needs to e controlled from a distance. Time spent in close initially is not right or him. Our natural thoughts are always to control them and touch them, but these things are not right for all horses at the beginning.
I know you are considering your horse and I know you will find a way. Keep us updated.