A variety of measures have been implemented along roads, aiming to prevent negative impacts on biodiversity or utilize potentials to enhance biodiversity. Testing the functioning and effectiveness of these measures is essential to make informed decisions in future road projects. Our objective is to test the effectiveness of a newly designed fence that aims to keep arboreal mammals off the road and guide them towards crossing structures. The fence is 2.20 m high and consists partly of a smooth surface – constructed of High Density Polyethylene (HDPE) – that the animals cannot get a grip on. The smooth surface starts at a height of 1.0 m and reaches up to a height of 1.75 m. The fence was examined by placing it in the enclosures of stone and pine martens in captivity. Three fence modifications were planned in case the martens managed to pass the fence: extension of the smooth surface to a height of 2 m (type 1), extension of the smooth surface to a height of 2.25 m (type 2) and adding a 0.5 m overhang to the type 2 modification, perpendicular to the fence and also constructed of HDPE (type 3). Days prior to the experiment, less food was provided to the martens in order to induce them to surmount the fence. Bait was placed at the top- and other side of the fence, and infrared cameras were used to record whether, how quickly and how often both marten species were able to pass the fence. The trials with stone- and pine martens were carried out in Biotopwildpark Anholter Schweiz (Germany) and Otter-Zentrum Hankensbüttel (Germany) respectively. Both species managed to surmount the fence. Stone marten passed the fence after 58 hours and 33 attempts and pine marten did after 24 hours and 3 attempts. After the fence was modified (type 1), stone martens were not able to pass the fence, but pine marten still managed to pass this fence type, already after 1.5 hours and 2 attempts. After the fence was modified again (type 2) pine marten also did not manage to get over anymore and attempts were ceased. We recommend to construct wildlife fences with a 1.25 m high smooth surface, starting from a height of 1.0 m and extending to a height of 2.25 m, if the aim is to prevent martens to enter the road corridor.