I have a 6yr old gelding that is ready for Advanced/beginners training, he knows walking and trotting and some jumping, he has cantered.
I am going to jump right in here. A horse that is walking and trotting and "has cantered" should NOT be jumping. Too green! Jumping, no matter how small the jump, is for a more advanced horse. Trotting over poles on the ground and teaching the horse rhythm, straightness, impulsion, balanced turns, transitions between gaits and in a gait all comes before jumping. The horse should canter easily and at least be able to do simple lead changes (two or three trot strides before picking up the other lead).
But we have two problems.
1- He stops at the curves of our "arena" (a flat piece of land). I think the piece is a 50ftx60ft, and I think its too small for his training. He stops at the curves if we are cantering.
This horse is too green to be cantering into a curve in an arena that small.
2- we don't have an arena, and since the 50x60 is too small for training, I was going to fence in a piece of land for a temporary arena, and use that.
You do not need an arena. You need flat ground that has nice even footing. Get orange cones to mark the area.
But, how small can I go for training cantering leads and circles most of all?
Anything about the same size as a dressage arena. But at this point in your horse's training you need to get him long, low and down.. stretching his top line.. seeking bit contact. You need him trotting well and keeping an even stride even on a turn. You need to be working circles, serpentines, figure 8 that are two circles that touch each other NOT two half rounds with an "x" in the middle. You need to be able to have this horse go from a walk to a trot with a touch.. not a single rushing walk step. You need him to go from a trot to a walk balanced.. not losing himself all over the front. You need him to extend in the walk and the trot. When you get that, you try cantering a straight line only (not curves). Eventually you add a large curve.
I repeat.. you do NOT need to build an arena. A surface is more important than a fence.
I am going to get a vet to check him out to make sure he's sound. If he is, then the reason I think he's stopping is because he doesn't have enough time to collect and prepare himself for the turns.
Again, how small can I comfortably get for training?
Again, any flat area will do. Footing over fencing.