Thanks bonjoy, so for the specific case of the Domes heel toes would you suggest superglue or anchor resin? Obviously there’s no hold to ‘glue back on’ it would be more about re-establishing a solid surface.
This stuff is expensive, but very good. Designed to make rotten wood structurally sound, it's a very thin 2-part epoxy resin that is very easily absorbed. Because it is so easily absorbed it doesn't leave a surface sheen until the thing you are treating has either become saturated, or you apply it in stages, letting each stage set first (so that the sealant makes the substrate less permiable). It's quite easy to back off before you get to the stage where the surface become covered. Not tried it on hold repair yet, but I've tested it on very old powdery brick and plaster and assume it would work just as well on rock. It should be a lot more durable than superglue.It does change the surface colour, making it a few shades darker, similarly to if it was wet.https://www.makewoodgood.co.uk/product/cpes-clear-penetrating-epoxy-sealer/
It’s certainly stopped eroding but if you really carefully compare the glue patch with the surrounding rock using your fingers then there is a subtle difference in the friction. The main grain is certainly still present but it’s enough that if it were a key sloper then I think it would make a difference to the problem.