Let's cut to the chase. Many beaches and islands ...
... have been ruined by dog walkers that don't clean-up. Low Island is a near by example, though the geese are as much to blame. Often there is a steady stream of dingies ferrying poches to the island so they can do their business. Small wonder very few landowners are open to dogs walking the shorline.
Though I know it is great to let a dog run, dogs and swimming beaches are inherantly incompatible. This is obvious. Clean-up doesn't change that. It's not what you want to spread your towel over. In part, this reasoning is also why Herring Bay is Zero Dischage Zone.
So while I am certainly not anti-pet, dog walking near the water is alway going to be a problem. Marinas are generally friendly. Using beaches is very poor form.
I don't think this is what you were suggesting. It just came to mind, having just visited a soiled beach.