Best way to teach a horse to move into trot

[Brambridge04]

I know some horses just get it, but my friend has a 12 year old cob who hasnt done anything for a few years, but was broken to ride previously, He will walk off from your leg but asking for a trot seems to be a nightmare and you can smack him on bum, kick him on, flick whip at him etc and he just carries on walking.....

However on lunge, he will trot from the flick of lunge whip and voice....

Been teeth/back/saddle/legs etc all checked....

 

[Brambridge04]

bump

 

[Headpiece]

Why dont you stick a rider on board and lunge him?

If ridden previously he might have got away with ignoring the aids until the rider gave up.