Quantifying the penetration depth of a dragging anchor on a horizontal layer of rockfill provides the possibility to optimize the layer thickness of rockfill layers with a protective function. Current research on this subject is limited and is often aimed at anchor capacities in sand and clay. Penetration behaviour in rockfill is mainly investigated for protections with a limited width. Anchor dragging tests carried out for a canal expansion project show that as the rock size increases, the penetration depth and the holding capacity of the anchor decrease. A semi-empirical prediction formula is derived. An additional series of scaled down tests shows that the process of anchor drag in rockfill is scalable, as long as all aspects of the trial design are taken into account. This provides possibilities for accessible further research, expanding on the prediction of penetration depth and further anchor behaviour in different types of rockfill.