A simple thing (in theory): a tile that the player can traverse but that animals can't. I guess it would be an item of craftable flooring. Apparently cattle grids don't work brilliantly well against goats, but one may perhaps allow the realism to slip a little. Horses can't pass them, though. I don't know whether it would be impossible to implement in SDV (or whether someone has already done it), but it would make life a *lot* simpler when planning gates and fences etc!