carrying straps for auxiliary oval shield

[Titvs Statilivs Castvs]

looks promising, but still where to put the furca?

So some kind of double strap arrangement, maybe? Unless the pilum is tied to the shield in some way... He appears to have both hands free though, so could feasibly carry a spear or furca in either if necessary.

something like that also crossed my mind, for testing i will try to loop two seperate ropes thrugh the handle of the clipeus and wich would end in two straps like the ones on a backpack

I do this and it works very good. However, not (consciously) based on any evidence.