Avoiding/Fixing Terrain Geometry Stretching?

I’m in the middle of a group project at university where I’m doing the majority of the engine work for a game level we’re creating, it’s partially outdoors and to save some time manually modelling it in something like 3ds Max, I figured it would be easier to sculpt the terrain.

However, not having done this before I didn’t really think too much about how it would work, and now that I’m thinking about applying a material to the landscape, I can see that there’s some terrible stretching on the UV grid-like material that defaults onto the terrain. This is mostly apparently on the many cliff faces I’ve got.

I tried using the retopologise brush to no avail so I was wondering if there was any way or fixing this or at least some way to avoid this if I was to resculpt the terrain again?

Thanks a lot.