Apart from a variety of useless stakes and having seen a beach tent dragged by a dog having great fun as his family chased him and his "kite".
The best we've seen is about ten metres of seat belt webbing and about the same of some light haeavy gauge polypop rope with the endstied making a loop that the dogs owners circled around quite large roack or looped to good sized bushes etc.
A few years back at Crantock a family arrived with two German Shepherds and a a large fold up water carrier that was fiiled by the dad with sea water whilst the kids quckly dug a big hole, the water carier was put in a canvas bag ( I guess to protect the water carrier) that went into the hole and the kids then covered it. The dogs were harnessed to the attached line for thwe day when needed and it held them.
End of day, the kids had a few minutes fun digging away the sand on top, bag pulled out sea water then dumped and away they went.
Good luck if this is any help, but can anyone tell us how to stop our dogs barking. If we try and leave them for a swim they just bark non stop as they want to join in.
Fine until we get "raked" by their claws nd paws ;-0