You can't own the land because you didn't make the land, but you do own the added value that you've given that land, as long as you have dominion over your fair share and no more. You may have done that by building a house on it, or at least buying the house that someone else built on it, by draining it, improving the soil and cultivating it. When you do things like that you're entitled to give it reasonable protection from ingress or damage, the key word being reasonable. Keeping people off vast tracts of moors and mountains so that ignorant men can shoot at stags or birds for "sport," or trying to keep me off beaches, doesn't come under "reasonable."