I am converting sections of my yard from lawn to other groundcovers. I'm doing this one section at a time.

I would like to put in a barrier between the grass sections and the rest, but there are a lot of trees with surface roots and I don't want to cut through them in order to sink edging. (I assume this would cause some damage to the trees, but it's also a LOT of work to dig a slit stopping every couple of feet to saw a chunk out of a tree root.)

If I laid a row of concrete pavers or something on the surface how wide of a row would I need to keep the grass from traversing it?

Any other suggestions for creating a barrier without digging?