Normally enforced by local council, but they are unlikely to bother.
We live on a fairly new estate, covenant restricts visible aerials and sky dishes. Reception is practically impossible with an in loft aerial (people have tried) so practically everyone has a sky dish.
Was some rumour amongst the local estate agents about 4 years ago that a new planning officer had moved into the area and was making his mark by stamping on people breaching covenants.
I suffered a shared access drive before (never again) and that was covenanted but theres naff all you can do bar solicitor, but then you need to declare a neighbour dispute if selling.
Personally I would park my car in that spot as often as possible to make them park elsewhere.