Only one way with a rockery I think and thats clear the whole patch of perennial weeds etc and lay down some landscape cloth over the area and cover with gravel, shale etc. When planting, cut a cross thro the matting and plant in the hole.

The spreading plants will root through the cloth and the large alpines will have room to expand due to the 'cross' cut.

This keeps any couch and dandi's from emerging and the annual weeds are easily removed as they have their feet only in the gravel. Rockery can then last for many years without that much attention.