How can I curb mating behavior?

[4Hforlife]

Okay, so my brother has 3 show rabbits that I primarily care for and his Holland lop buck loves to mount and hump my arm when I put my hand in the pen and recently he's taken to chinning everything he can, myself included. He doesn't hump anyone else. Just me. How can I detour him from this behavior?
He's the same age as our other buck, a mini rex, but the rex never got like this except for the one time at fair when we learned he was male.(he was trying to mount the judging table)
I know the easy answer: spay/neuter. But this is a show rabbit so he has to be intact per ARBA rules and he's too nice a rabbit to remove him from the show string.

 

[Augustus&HazelGrace]

When he does this push him off and place your hand on his back and apply pressure do this for a few seconds and let go but make sure he is not struggling to get out of it when you let go. By putting pressure on his back this shows him that you are "top bun" and do this every time he mounts your arm and eventually, he will get the idea that you are "top bun" and he will quit mounting you.