out. James Hoy in The Cattle Guard discusses four kinds of electric guards. One that was patented in Illinois in 1955 and another invented in New Zealand in 1979 are similar; each resemble "something like the framework of an old-fashioned metal bed" connected to a battery or high-powered fence charger. They are easy to drive across, but may pose a danger to children or animals that get stuck in the guard. Another type was patented in two versions by an Oregon inventor in 1956–57; it consisted of 20 current-carrying synthetic rubber strips mounted on a wooden frame. The invention proved highly effective in deterring all animals, including dogs, and it was maintenance free, easy to drive over, and safe. However, the company that acquired the manufacturing rights stopped production in 1960. A fourth type, homemade, consists of two sections of woven wire or steel plate laid on a concrete slab and set apart from one another on either side of a fenceline. The wire sections are then connected to an electric fence or to a separate charger, either conventional or solar-powered. Effectiveness on wildlife While cattle grids are most effective on cattle, they can be used to exclude deer and elk. Research has shown that deer can cross cattle grids with flat, as opposed to rounded bars. Sometimes a cattle grid is doubled to exclude these animals. A cattle grid requiring a horizontal leap of is considered effective when combined with a deer fence. Striping is also painted on roads as a visual deterrent to deer, as with "virtual" cattle grids. Limitations and risks While these barriers are usually effective for cattle, they can fail due to ingenious animals. Sheep searching for food have been known to jump across grids, step carefully into the spaces, or run along the side of grids as wide as . Wider grids are used where wildlife is to be contained. Some animals can jump across them, and a barrier that stops deer needs to be at least wide. Bison, and bulls in particular can easily jump across an barrier, and have been known to jump widths of up to . In areas with heavy snowfall and long periods without a thaw, snow can accumulate beneath a grid and allow animals to walk across. Horses are particularly vulnerable to cattle grid injuries, as their single-toed hooves can slip between the bars and trap their legs