Blending two textures on a model

Hi all,

I'm a bit stuck, basically I want to blend two textures together on a model, so the grass slowly transitions into rock instead of having a hard border like in the picture below (similar how you can with texture paint on unity terrain), I cant use unity terrain as the object will be moving, not square and above the actual ground.

The thing is I don't want to make it all on one texture on the model (grass and rock) as the grass will be tiled and the rock will not be. Obviously I don't want to separate the objects because I want the blend between the two. On a few threads I have seen references to some what seem to be outdated scripts that manage this, but I figured I would ask here just in case it is something built in that I am missing.

Thanks

Kel.