<p>A: A border security fence being constructed along the border between Slovenia (SLO) and Croatia (HR) separates all three large carnivore (LC) species in Slovenia from the core population areas in the Dinaric Mountains, impacting their long-term viability, severing the Natura 2000 network, and decreasing the potential for natural recolonization of the Alps. B: The expected effect of the fence on brown bears. Points are individual bears, genetically sampled from bear mortalities between 2003 and 2013 (<i>N</i> = 1,414), which we genotyped using 20 polymorphic microsatellite loci. Lines showing full siblings or parent–offspring relations between individuals demonstrate that the border between both countries, where the fence is now being constructed, had, up until now, no effect on movement and gene flow in this bear population. The Trio ML method (Wang 2007) was used to estimate relatedness. Lines show <i>r</i> > 0.45. Darker lines are assignments only for bears sampled in 2012 and 2013 (<i>N</i> = 296). C,D: GPS telemetry tracks of lynx (C, <i>N</i> = 11) and wolves (D, <i>N</i> = 28) show that these animals had no problems crossing the border before construction of the fence, and even had home ranges that straddled the border.</p