The only reason to add sand to your grow medium is to improve the texture and drainage. But if you try to grow in it you must consider it to be a soilless medium and treat it like hydro. But if it were good for hydro, hydroton would never have been invented! So no, don't bother.
The plant growing in your horseshoe pit is doomed anyway. The only way it will survive is if it roots far enough down to find proper soil. Oh uyeah, and doesn't get mushed by a shoe.