When I coach riders I often put some kind of marker or markers in the arena. A cone is the most common marker I use but I have been known to use anything available including buckets, rocks or random manure piles. These reference points help me, as a coach, to communicate more clearly to the rider. If I ask the rider to circle to the right while staying thirty feet from cone we both know the goal. It isn’t important to me if the goal is met during the ride but having the clear goal gives me, the coach, a point of reference when discussing and measuring progress.
Having a marker is also helpful for the rider when the coach isn’t around. The clear goal helps the rider focus and measure their progress even when the coach is not available.
As a professional rider myself I am very aware where my horse is stepping at all times. This awareness didn’t happen overnight, it came about after years of riding with specific goals, and markers, to measure my progress.