
There's a beach near St Ives at Lelant called Porth Kidney that is perfect for dogs and no restrictions, we make a point of stopping off there when ever we're out and about. if you ask some one for directions to Dynamite Quay you'll be able to park right on the beach, or just head for West Cornwall Golf Club and you won't be far away from the beach. If you get stuck for directions, PM me and I'll send a link to the map for directions.
On Hayle side of The Saltings is The Towans, very popular with local dog owners so can be busy at times.
Further up the coast towards Newquay which I would avoid like the plague is Holywell Bay, no dog restrictions and has freshwater running across the beach.
Going back the other way towards Penzance is Long Rock, again no restrictions and with parking along side the beach.
Kerrier district council has some beaches with dog restrictions others with out, After 7.00 pm there are no restrictions on any of Kerriers beaches but the dog warden does patrol and issues fixed penalties to those who "forget to pick-up"
Not a definitive list by any means.