We had Walkers for 10 years before we switched to the Marchador. The reason Walkers are difficult to gait correctly is that for the past 50 years the breeding has not
been for a correct running walk but for a pacey horse, as the pace is easy to "square up" with devices.
We had a few old blood Walkers (that predated Merry Go Boy). They displayed a small range of gaits, too, but that range was much
closer to the center was was much easier to work with. You can move a horse a small amount of the continuum of gait with training; to move it a large amount you'll have to resort to either devices or very strong training practices. And when you're done if you remove the device/strong training the horse will revert to it's native way of going.
A friend in Brazil, to simplify discussion of gait in a breed where three gaits are permitted, came up with this:
Pace L4 L3 L2 L1 Center D1 D2 D3 D4 Trot
In this diagram "L" means lateral, "Center" means an isochronal four beat gait, and "D" means diagonal. Pace and trot are self explanatory.
Using this scale we get away from some of the terminology confusion that runs through the gaited horse world. This scale can be used to describe the gait of any horse (trotter, pacer, or in between).
Every horse has a "native way of going" that can be placed on the scale. Ordinary training can move horse one number of the scale without too much difficulty. But moving more than one number will be much more difficult. This is why breeders should aim for the center. If they do thier job right then even if you produce an L1 or a D1 you can easily train to the center.
This presumes, of course, you want a centered gait. If you're breeding speed rackers then you don't want a centered gait, you want something near L4. If you want to breed softer gaited eventers, then you're going to be looking at producing a D3-D4. If you have no idea of what your doing then God only knows what you'll make in the breeding shed.
Given that the vast majority of Walkers are going to run L2-L4 bringing them to the center will be difficult. If you go the traditional route (ride a la brida,
strung out, and use a powerful curb to control the head) then you will at best achieve a "false collection" and a false running walk. If you correctly collect the horse, get a neutral to slight bascule,
and sit centered then you'll pull the horse to the center as much as it will be able to go (without resorting to devices). But when you relax the horse will relax, too, back to its native way of going.
For the past 20+ years the most asked question in the Walker world is "how can I get my horse to do a running walk?" That this is the most asked question is a serious condemnation of the Walker industry as a whole. There are a few folks who understand this and try to produce genuine Walkers (we dealt with them over the years) but the vast majority are what they are (pacy critters who will need serious work to perform the running walk). This is less a condemnation of the horse than the evil triumvirate of the TWHBEA, WHOA, and WHTA.