Traditional mitigation measures against debris flows may involve construction of expensive structures such as sediment retention basins. Flexible ring-net barrier systems provide a new lower-cost alternative and have already been successfully used to stop small flows. They also have the potential to partially dewater and stop large flows. Our goal is to document the performance and optimize design procedures for flexible barriers using full-scale field tests. The Illgraben catchment, Switzerland, delivers ~5 large debris flows per year following intense rainfall events. Flow depth and front velocity measurements combined with bulk density data from a force plate allow determination of the potential loads produced by debris flows as they approach the test barrier. An instrumented 4 m tall ring-net barrier was installed ~50 m downstream of the force plate in 2006 and was soon filled by a debris flow. The full net was overtopped by many flows in the following months. Here we discuss both the first event that filled the barrier and the subsequent events. The over-topping events are of special interest because they suggest that such barrier systems may be suitable for long-term field deployment.