Hi Simon
I think this spot is called 90 mile beach we went to just after christmas this year (or last year, what ever you want to call it)
On the Coorong road from Tailem bend to mount gambier there is a spot called salt creek (A servo with a camping ground).
Go into there and you can get all the info about the area from there.
Straight across the road from the servo there is a dirt road, take that road for about 10 kms.
Then there is a right hand turn that will take you through a very short track onto a dry salt bed. when across go straight up to the beach,
or turn right into a big grass area that you can also camp at. Nice area protected by a mother of a sand hill from the wind. $5 a night per car.
Going up the sand hill is time to let your tyres right down.
Once on the beach you can turn left (we didn't go that way) or turn right and head towards the murray mouth outlet.
Its about 90 kms down & 90 kays back. First 15-20 kays down is very soft sand, after that it hardens up quite well.
You can also camp on little cutouts in ths small sand hills. Little bit blowy though.
We stayed one night on the beach and one night in the grass camp ground.
Lots of people down there fishing but is a big area so not that busy.
Dogs would not be a problem.
I think the beach is closed a certin time of the year for nesting or something but it was opened up a few weeks before we went through.
It would still be open now till probably june or something like that.
If not that area i recomend robe to beachport, Excellent 4wdriving. Would be very bust that weekend though
Here are some photos of the 90 mile beach