For those that say round pen this gelding then I can assure you that some horses are not safe to round pen. I certainly would not want to be shut in with it.
It takes an experienced person to work with this sort of animal and, with some there is no hope and euthanasia is the best way for all concerned.
I had a big warm blood mare come here in an emergency situation as her owner had been in a bad car smash.
I knew nothing about the mare only that she was turned out and not ridden. I was warned by the driver delivering her that she had 'a reputation' and had been to several places for training but returned shortly afterwards.
She led out to the filed fine and I turned her out with two of my mares. Usual squealing and threats and my two mares went off and she was a distance behind them.
Later I drove the ATV to the field to feed them. My mares came to the gate as usual when they heard meals on wheels I went to unlatch the gate and the new mare charged me and really meant business.
I will admit I was taken aback but, all I did was to turn the ATV around and drive back to the barn whereby I picked up my twitch, about 4 ' in length and made from a broken pitchfork handle.
Back at the gate the mare came at me again, this time harder and she actually bent the metal gate.
Difference was that I was ready for her and hit her straight down the front of the face with the twitch. HARD.
She shot off and stood about 50 yards away shaking her head and yawning. I drove into the field and across to the area I fed. Put the feeds out. New mare stood back and when I drove towards her she ran off.
That, to my way of thinking was good. She had a fear of me.
Next day she kept away so I caught my two and led them in letting her follow into the big loose area we have in the barn. I then had her go into a stable. There was no sign of her thinking of attacking me - she just wanted to keep a safe distance from me.
Once in the stable I caught her and decided that I would see what was causing the problem.
She was misaligned but nothing major and I soon adjusted her. I bossed that mare. If she so much as blinked without permission she was corrected with a hard poke of my finger, an arm wave or harsh voice.
I called the owner's husband and asked if I could ride her - after getting her feet trimmed. His answer was that no farrier would work with her but I could ride her if I wanted but he would not take any responsibility.
My farrier came and she started to mess but a poke and hard word from me and she was fine. My farrier had refused to do anything with her a few months before, he recognised her but said nothing knowing that A) I would have sorted her and B) I would not object if he cracked her one if she deserved it.
I did ride her to find that all she did was rear. I just sat her out and a few minutes later had the ride of my life on a very well trained horse that was answering aids I did not know I had given. Piaffe, passage, half passes were all there.
When I rode her out on the roads and tracks she was worse than any of my youngsters for spooking and bewilderment at new things like sheep and cattle. However, she did enjoy it and the more she went out the better she got and braver. She had a good pop to her over hunt jumps and ditches.
When the owner returned it was to find her 'baby' a totally different horse. Happy, relaxed and enjoying life. The story was much as I had suspected in that the horse had been bought for the price of a house, as a three year old in Germany. She had been trained for dressage and done nothing but twiddle around in an arena for about 8 years, I reckon tat she had had a mental breakdown and aggression was the way out. (She had hospitalised three people) When she meat someone who gave her as good as she was giving she had to think twice about it and make a decision that if she attacked me then I could and would retaliate and hurt her back - just as another horse would.
Now, the punishment fitted the crime, it was applied at the instant she went for me so, there was not an iota of doubt what it was for - so, it was fair.
I sold the horse for the owner and she is now fox hunting and show jumping and loving life.
I have only, in many years, come across three horses that were truly vicious - the first was sorted in much the same way, the second was put down, he was a real nutcase and I would have loved to have had him for longer but he returned to the race trainer for their open day and when the horse busted through the stable door and attacked the Head Lad, chasing him into a garage and the horse rearing up smacking his head through the roof, there was little other choice.
The third was the mare above.