Hind Quarter Muscling

I want to get Chance some better muscling in his rump, and the area he is at has some hills including a spot that's been dug out (its a lifesized chessboard with little hills surrounding it), and I was thinking if walking him up and down or jogging in hand would give me the desired effect?

I realize it might work best under saddle, but he is super spooky currently, and my instructor worries he might bolt for home if given the chance. So for my safety, ground work is best option available.

I am thinking raised cavalettis might help, too? And transitions when under saddle?
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