When you build a vinyl fence you have to make sure that the posts are inserted deep enough in the ground. Wood and metal fences have weight behind them that helps keep them stable. A vinyl fence is not that lucky as vinyl is a very light material. The posts of the fence are there to maintain the stability and if they are too close to the surface they can be ripped out of the ground by a strong wind or an animal. A wood and metal post does not require the depth that a vinyl one does. As a good rule of thumb you should create a hole that is twice the depth of what you normally would dig for wood or metal. This will create the stability needed to keep the vinyl fence standing.