Your eye for a stride improves the way any perceptual skill improves: honest repetition with feedback. These are the exercises we would actually set, on the horse and off it, roughly in the order we would set them. None of them needs big fences; most of them work better over poles.
Short on saddle time? Streyed is a training game that gives your eye hundreds of scored approaches an hour in your browser, so the arena exercises below land on a trained eye.
Try it freeOn any approach, to a pole or a fence, say the strides down as they come: four, three, two, one. Saying it forces you to see it, and being wrong out loud is how the eye calibrates. Start counting from three out; as it gets easy, start earlier, until you are calling the distance out of the turn. This costs nothing and you can do it in every canter you ride this week.
Set two poles on a comfortable four or five strides for your horse. Ride the line on that number until it is boring. Then add a stride, then take one out, on purpose, from the rhythm, not from a last-moment kick or snatch. This is the producing half of the skill: an eye is only useful if the canter underneath it can act on what it sees.
One modest fence, met again and again off the same circle, in the same rhythm. Because the track and the pace stop changing, the only thing left to learn is the look of the distance arriving, and it starts arriving on its own. This is the exercise that most reliably turns "sometimes I see it" into "usually I see it".
During all of it, look at the middle of the top pole and nothing else, from as far out as the turn. It is much harder to judge a target you are not looking at. Let the ground line and the strides stay peripheral; hunting the take-off spot on the floor is the habit that produces last-second lunges.
The limitation of every arena exercise is volume. Horses have legs, arenas have opening hours, and each repetition costs the animal something. But the recognition half of the skill lives in your eye, and it trains anywhere you can watch approaches and be told whether you were right.
That is what Streyed is for: a schoolmaster called Napoleon canters and jumps in your browser, and eight levels ask you the questions above, from holding a rhythm to calling distances good or off to riding a full course, with instant feedback on every approach. Start with a free day.
Little and often beats occasional marathons. Ten focused minutes of counting down, or one pole exercise ridden well, does more than an hour of jumping around hoping. Expect the eye to sharpen over weeks, keep improving for as long as you keep looking, and fade a little when you stop. If it will not come at all, the cause is usually rhythm, and why can't I see a stride covers that.