Elfyn has it exactly right - collect the evidence and make it easier for an investigating officer. Nearly all of us own a camera of some description and can easily take pictures. That alone might deter some people from letting their dogs run riot. Follow them back to their vehicles and get their numbers. I would strongly advise caution in confronting dog owners. They seem to lose all sense of reason and remember often regard the animals as their children and therefore beyond criticism. I know of members of staff of conservation bodies who have been physically assaulted when trying to reason with dog walkers. As usual it is not the dogs but their irresponsible owners.
Signs alone will not make a difference as people will blatantly walk past them and then swear blind they never saw them. Wardens of National Nature Reserves need to be encouraged to educate behaviour on protected areas.
CCW are charged with upholding the protection of our wildlife and the CROW Act made it easier to prosecute third parties for damage to Sites of Special Scientific Interest. I may be wrong but I cannot remember one instance of them taking a prosecution. To my knowledge there are a number of places where they should regarding ongoing damage.
If we as birders stand up to be counted and give them and the Police the evidence maybe things will change.
Derek Moore - a concerned neighbour