Made by petpeek tm, these windows are for animals living in the confinement of a back garden; they may be installed at any height and if you have several animals in the yard or want to provide a more varied view, you might install multiple windows.
For chicken coop maybe. Patio stones around the edge of the fence makes it hard to dig under. Great idea for the outside of chicken coops and garden fencing too. Would also keep weeds from growing up into the fence.