Park at Goring on sea, making sure that the tide is out. Check this link

 

While looking out to sea turn to your Right. 

Not too far down the beach there is a pleasant cafe. See link

 

There is parking at the cafe if you prefer. Also toilets and water for the dog.

After the cafe there is a wide grass path that runs for about a mile. If you wish to go further you will have to go onto beach  before the grass path starts again, it finishes just before Rustington.

If you park at the cafe it is a good place to take elderly relatives while also exercising the dog.

Don't forget to take fresh water, though there is a very kind person who usually puts out several bowls not far past the cafe, and there is an outside tap and toilets at the end of the first grass path, near the hotel.