Prevent Textures from being deformed

Hello Blenderartists community!
I´m using Blender a while ago (newbie) and are doing my first “big” project.
I have an animation with a mesh getting deformed by a Boolean object. The mesh is complex, so I can´t use the generated UVs and had to do them myself. I now want the texture using the UV map NOT to deform when the mesh deforms, kinda like stretch the texture/UV instead of deforming it.

Thanks all of you beforehand.
NGCHunter2