I work for a rescue organization and I also own a rescued horse. Biggest Mistake Ever is letting their past become an excuse.
My mare has ALOT of issues because of her being "babied" after she was rescued by her last owner. She was fed straw and bread and was left in a pasture to fend for herself with no shelter. So her last owner felt sorry for her, brought her home and spoiled the crap out of her. After a while she started to become very disrespectful and dangerous which is one of the main reasons her last owner had to get rid of her (and how I ended up with her). She has a ton of bad habits and was allowed to get away with everything because she was "cute" and neglected. I now have my hands extremely full, not that I would change adopting her for the world
I love my mare but it has been a lot of hard work and frustration and injuries, luckily nothing major. And all the hard work is paying off.
Another personal experience which I contributed to without realizing, is one of our rescues at the organization, who had never ever been handled in her 3 yrs of life. So when we could finally handle her, she was of course spoiled. Now I have to run off a 16 hh TB every time I go into the pasture because she will run you over for attention and will attack the other horses for attention as well. I have been caught between her and my mare and its not a pretty or fun situation.
When you said he was a rescue, that right there is the problem. It is not his fault. Its people`s attitude towards him. Treat him like any other horse, stop making excuses and I bet you see a huge difference in him.
And again MAKE THE BO TAKE RESPONSIBILITY FOR HER/HIS DANGEROUS HORSE BEFORE SOMEONE GETS SERIOUSLY HURT.
There is never any excuse for kicking or biting (my 2 biggest pet peeves) and disrespectful horses should not be used for lessons or allowd around people who can not handle him. Maybe you should just switch barns. Sounds like the BO is closing their eyes to this situation and ignorance is not always bliss.
I really really hope no one gets hurt <3 Good Luck Minnibee