Posted: Tue May 17, 2022 9:17am
Dogs are not allowed at all on beaches between the beginning of June to the end of September & the police do patrol to enforce this. Outside this period, though officially dogs shouldn't be walked on the beaches, there are no patrols & you will see dogs, especially from the campers on the many camp sites.
If you drive, then Playa de Brosquil (the far side of Gandia) was a designated dog beach, though I recall that this was going to stop & it's not on the updated 2022 list on Red Canina: https://www.redcanina.es/mapa-de-las-playas-para-perros-en-espana-2016/
Try the Parc Natural de la Marjal de Pego-Oliva just outside of Oliva.
Do keep your pooch away from pine trees during December & April when the processionary caterpillars are active.