Passive mob roaming lure

Passive mobs should be attracted to hay bales or a special new block and stay within a certain radius of one. Fences are great, but some builds lend themselves well to cage-free animals. For example, I built a mountain and put goats on top. Currently, to prevent them from leaving the mountain I chained them to a bush. What If I could put a block somewhere hidden on the mountain so the goats would stay up there? It just seems like a really nice quality of life feature for builders looking to incorporate nature into their builds.