Anyone know how i can control my extremely low functiong highly aggresive autistc brother?

he is 15 and is about 5.9. thz to synergy he has the strength of 1 and a half men. he can become aggresive at the drop of a hat over somthing as simple as he wanted the water you were drinking even though you just gave him 2 big glasses of it. (real situation happend yesterday) and when he goes bonkers he can literally bring you down to the ground with one hand. and nothing we do seems to calm him down. hes on meds and they do absolutly nothing. his psychiatrist who is supposed to be the best in our state has absolutly no personality and her only advice is to put him in an institiute. and that was on the first day she met him as a lil boy when he wasnt so aggresive. the only reason why we are still with her is because noone else will take him. weve tried other and they gave the same song and a dance put him in a home. were at wits end, and we dont belive in putting him in a home. and as for things weve tried at home, weve tried an art and dance, program for autistic kids and that turned out to be a total joke. we attempted to try the whole horse back thing but before we even made any appt they said it wasnt a good idea since he was aggreisve and could spoke the horse. and we tried the whole glutein free ting for about a good 3 months. but not only did we see any results it was coslty for. keep in mind were not the richest people. and as i said in the question he was diagnosed as low functiong, highly autisc i belive somthing to that effect. so do you have any kind of possible idea that i could do to help my lil brother, hes getting older and stronger. any at all suggestions would be great appreciated.