Just the beach not accommodation. Thought it might be nice to go to a beach somewhere. Nearest coastline to me is around Weston Sur La Mud, Brean etc but they have problems with sinking mud/sand at low tide so looking for something a bit safer either Dorset or not far from the bridge into Wales.
Or a water park with safe entrance for swimming for the dog might be good. Or if anyone knows of a really quiet secret cove without other people that would be even better ;)

There is a nice beach for the dogs at Kilve. Kilve is on the A39 between Bridgewater and Minehead. It is a rocky beach that has a stream coming onto it which is deep enough for the dogs to swim in. When we have been there it has been very quiet, only us and a couple of other people with dogs, I don't know what it is like in August though. It is  a beach that is off the beaten track tucked away down a lane in Kilve but is signed off the main road, quite a small sign  and easy to miss. If you ever go to Pembrokeshire there are some really lovely dog friendly beaches there, but probably a bit far for a day trip :) .

Lots of great, dog friendly beaches in South Wales.  Two of the best that instantly come to mind are Newton Sands & Rest Bay near Porthcawl.  Newton Sands has total access, Rest Bay dogs aren't allowed on the first cove but after that it's a dog paradise.  RB is so huge that even on a busy day (when the tides out) you find yourself on huge stretches of deserted beach.  There are enormous rock pools as well as the sea for dogs to swim in.