Arena base help

Need the hive mind here. I have a sand/clay arena with a red clay base. Unfortunately, one area of the land has grey gumbo clay UNDER the arena - under the base- underground. WHen it gets wet, this clay has the consistency of putty (and its sticky like that too). Hooves go right through the base and into the gumbo clay - Of course we did not know it was there when the arena was constructed, and there is no other place it can go, and the irrigation is already in.
So I am looking for ideas for solutions. We have tried digging it out and filling the spaces with crushed concrete - but the gumbo seems endless and bottomless.
And ideas?

Not an expert by any means, but maybe you could spot-patch over the area with one of those mud grid products, maybe combined with some sort of rock underneath too? The grid will distribute the load over a bigger area and maybe prevent the breakthrough.

I had a similar thought because I’ve been looking at these mud grids for some wet places on a trail I want to make.

thanks. @wsmoak and @Heinz_57 I had been thinking about that sort of item, and wondered if anyone used it successfully and if so, just how much coverage is needed - I wonder what size area I’d have to cover, and I wonder about the “edge” where this meets the “normal” clay base… so many questions…