Weed matting.
 

Weed matting covered with bark or gravel prevents weeds from growing upwards
BUT windblown seeds from weeds landing on the gravel or bark will grow and
their roots will go through the matting's pores making the weeds well
anchored and not easily removed once established.

My front garden has raised beds which are surrounded by nearly 10 cms of
14mm gravel chippings. Anything growing through the chippings is so weakly
rooted in the soil beneath that removal is easy. Prior to the gravel and
raised beds, 15 cms of grass turves and soil was removed. the tuves are
rotting down nicely and the soil was used in the raised beds after mixing in
some grit, peat and compost using a cement mixer.

Geoff