I have a 12 year old otqh. He was already started on the pattern when I bought him 6 years ago. He's been on it off and on over the years. we had to figure out some saddle fit issues and get ulcers under control. But he's ready to go now. He knows the pattern and slow lopes it well. He's been exhibitioned and to fun shows. But I can not get him to speed up at all. Preserving his mind has always been my number one priority so I don't necessarily want to kick the crap out of him with spurs or use an over/under. I was hoping with time he would naturally pick up speed himself but it hasn't happened yet. Any ideas to encourage him? 

When I take away speed from a barrel horse for whatever reason I add it back away from the patterns. If they are mentally fragile or were I give and take away.  In other words I will get the horse in an open area or on the rail of an arena and work into a lope then gallop, come back down to a lope then try to smooch up to a faster gallop to a run, then come back down to maybe a trot, then smooch up from a trot to a run.  It doesn't happen overnight with some because I have been taking speed away now I am giving them permission to have it back and they are like what??  When I ask for speed I try to establish a cue to go with it like move up into a two point position then kiss.  I will though if all else fails take my over and under lightly swipe across their hips with those cues or maybe ride with a long dressage whip that reaches to their hip that I can lightly tap them with. I like to use my boot tops to encourage excelleration too with the ones that pick it up easy.  I learned that trick from Les Vogt.  Instead of kicking squeeze with your boot tops to the level you want your speed.  If you are wearing ropers you will have to pretend to have boots at your calves or maybe english riding boots...lol.