Whether you are allowed to or not, I would put up signs saying that dogs MUST be kept on leads and that any dogs running around near sheep may be shot. Don't use the term worrying, it is misunderstood to mean hanging by it's teeth from a sheep's throat, anything less doesn't count
Also townies think because we use dogs with sheep it's all a load of over-egged grumpy farmer nonsense- true, I've had apparently intelligent townie friends express this view at my kitchen table
The most effective signs I ever saw were in the Lake District listing how many dogs had been shot
I suspect it was bluster but it made us hang on even tighter than normal to our dogs ( we were (responsible) townie fellwalkers in those days).
Whose going to make you take down the notices? Anyone short if the Police, ignore. If they turn up you can ask them what they're going to do about the dog problem!