Well, if you are doing layering for propagation purposes you can just put a heavy rock on the stems so I imagine that would work for your purposes too. If you want wood you could try pliable spars made from various shrubs, such as are used in thatching.( Hazel is used here). https://www.brandonthatchers.co.uk/product/twisted-spar-bundles/

Hi Floral, a very interesting idea. I"m not sure if I explained well enough, because I'm not doing any layering or anything like that. I just want to direct stem growth to needed areas, then the Rubus will handle it's own layering (one layer will allow some weeds through). So the clamps only need to be 3-5 cm deep and 1.27 cm wide ( (1.5-2" and .5"). I'd like to be more gentle than a rock; the stems in less sun are a little soft for that).

In the end, I could try and find a wood worker and have them made, but I'd rather not with COVID out there.

Get some old fashioned hair pins (not bobby pins). Should be available at any drug store. As long as they are not pushed down tight enough to damage the rubus stems, they will do the job perfectly well.

btw, this is one of my favored groundcovers as IMO, it does the best job of suppressing weeds of any common GC's. However, it is very directional in its growth habits and I have not found it very easy to convince it to grow in a direction it does not already have set in its little plant brain :-) Pegging it down may help.

Hair pins:

Great idea. I like the sturdiness of this cover and that it re-roots all over. I can even step on it a little. And leaves of all different sizes too.

You explained fine. I knew what you intended. I just compared it with layering because you wanted to direct the growth but also expected the runners to root as they went. Rooting from stems is layering.