Creating a dust bath pit for guineas

[gguineasfamily]

I'm thinking of giving the guineas a belated Xmas present- a dust bath spot! So far most areas in the yard have clay, rocks or grass (or all 3) and don't make very good dust bathing spots. So I'm thinking of making a dust bath pit on top of the clay near the coop. I want to border it with logs to stop them spreading the soil but my mum said they would trip over the logs when fighting. Another thing I want is for it to be big enough or long enough for fighting rivals to be able to dust bathe at the same time. Would one dust pit or multiple dust pits be better? And border with logs or not? If I make lots of small ones I could put them in truck tyres.

Any ideas will be appreciated.

Thanks!