Summary Exclusion fencing is being increasingly used to protect areas of high conservation value or to create ‘islands’ of protected habitat for native fauna. The objective of this study was to test a range of fence designs to assess the optimum physical and/or electrical barrier required to exclude feral Cats (Felis catus) and Red Foxes (Vulpes vulpes). We tested against six fence designs by placing individual animals (18 Cats and 18 Foxes) in 20 × 20 m pens and recording their responses to various fence components. Fence design 1 was 1.8-m high with one electric wire at 1200 mm and another at 1500 mm offset by 80 mm and a curved overhang 600 mm in diameter. Fence design 2 and 3 had single electric wires placed at 400 mm and 1700 mm, respectively. Fence design 4 had a single electric wire at the end of the overhang. Fence design 5 had no electric wire and fence design 6 was 1.2-m high with an overhang and no electric wire. Neither feral Cats nor Foxes were able to scale the 1.8-m fence regardless of the position or absence of electric wires. One Fox and one feral Cat successfully breached the 1.2-m high fence by jumping onto the overhang and climbing over. Four Foxes excavated holes underneath the fence and one chewed through the mesh. Results from this work indicate that fences designed to exclude feral Cats and Foxes should be 1.8-m high, have an overhang that is at least 600 mm in circumference that is curved or shaped in such a way that prevents animals climbing over from underneath, and have an apron with a mesh hard enough to prevent Foxes chewing through. Exclusion fences do not require electric wires. The omission of electric wires will provide significant savings in building and maintenance costs for exclusion fencing.