If it is a restrictive covenant (for example, one saying the land cannot be used except for certain specified purposes) it is usually expressed as being for the benefit of whoever put the covenant there - normally the owner of neighbouring land. The covenant either has a time limit specified in the deed which created it, or is indefinite. If the latter, it can in theory be enforced for ever but if the person or organisation for whose benefit it was put there no longer exists or no longer owns neighbouring land that could benefit from it, then enforcement action is virtually impossible. What often happens then is that it is possible to buy quite cheaply an indemnity insurance policy to cover the risk of a claim being made.