My friend and I have just taken on loan a 3yo gelding - he is a lovely boy, very trusting of humans

He's currently about 14.1hh, Welsh D cross, gelded young.
He was advertised as will hack out alone - o has taken him on 1-2hr hacks alone, but he has recently started rearing upon leaving the yard. To my mind 3yo is too young to ask that of him. We also had his tack checked and it will have been hurting him.
So we have started taking him for walks in hand down 'the lane' but he is still very reluctant, keeps planting his feet and refusing to move. I know he's telling me it's scary and it hurt last time he did this, but to my mind if we can get him to do it a few times without anything bad happening then he may stop planting himself. Today I took him out in hand and made a loop out of the end of the lunge line, which I put round his bum, to get him to move forward. Obv I released pressure as soon as he took a step forward.
Also once he started walking out nicely I'd ask him to stand, then give him a treat and a fuss
On the way back up the hill to the yard I asked him to stand every now and then which he did - also asked him to a couple of circles away from home - needed the bum rope again, but his reward was the release of tension and being able to walk towards home.
Owner also only gave him a bucket if she thought he'd been good!? So friend and I are going to set a routine where he gets a handful of chaff plus pink powder whether he's worked or not, and always around the same time of day

I'm just desperate for advice on how to do right by this special boy! He's gonna be a stunner, and he's such an impressionable age right now... Please help me dear experts
