In reply to James Malloch:
There isn't much that's tidal on Portland - some parts in the middle of Wallsend and then much of Coastguard South - but both are guarded by boulder beaches which may be difficult for your dog anyway, I'm not really an expert in the limits of dog friendly terrain!
It is going to be pretty warm this weekend with wind a bit easterly.
Blacknor North hangs onto the shade the longest, until 1-2pm, and has a decent range of options up to about 7b-ish. Lots of nice stuff to do around reptile smile and all that sector.
I have taken my son (now 5) down to Battleship Back Cliff and Battleship Edge a number of times. The Edge will be hot once the sun hits, as will some of the walls on the back cliff, but the cliff base holds the shade better and the wind can funnel down the gap between back cliff and the block to take the edge off the heat.
Coastguard North has fairly ok boulder beach and a short approach so I would have assumed might be ok with a dog and is right near the sea which will take the edge off the temperatures.