I'm a little confused by what you're asking, OP. The number of strides in a ling, gymnastics, bounce, etcetera are always predetermined. Strides BEFORE a fence can be unlimited.
If you are working on seeing distance, I would suggest working to know three strides out. You can start small, by announcing (out loud xD) when your horse is going to take off. Call it "one". Once you've got that down, try counting one stride back. "One, two." Two would be the take off. Next, try for two strides back "One, two, three." Three would be the takeoff. Finally, from three strides back. "One, two, three, four." Four is the take off.
Three strides back is typically how far you need to adjust a horse's stride, if necessary. This gives you time to ask, and your horse to deliver, a lengthening or shortening of stride so as not to knock poles or split legs, both of which will dock you points depending on the discipline.
Another good way to find distances is to use ground poles and work on not splitting legs.
The sensitivity of the internet baffles me.