Safety can easily be achieved by choosing the right material. People often think it is cruel to lock your horse behind an electric fence. In fact that is one of the safest means of fencing because an electric fencer does not give out a harmful shock people can easily handle the same shock and a horse out weighs us by 800 pounds. Imagine the shock being 80% less, you would hardly feel it. It is just enough to make them aware and teach them to stay away.
Electric Horses fencing can be made of 2-5 strands of poly tape, electro braid, or high tensile fencing wire 2 strands is enough for a horse but many people decide if they are building an electric fence they might as well add a few wires and prevent predators such as coyotes or wolves from bothering their animals. The only precaution with any type of wire is the possibility of tangling around the horses feet and becoming dangerous. Routine checks of the fence should be made ensuring that the fence remains tight preventing any possibility of your horse walking on it.
The second proffered method of horse containment is a three or four plank or rail fence. These fences require minimal repairs and are the most decorative giving your yard a true ranch style, but cost the most to build. Nails or limbs sticking out can be dangerous.
There are many different types of fences built for horses but the two I just discussed are the most popular and most importantly create the safest environment for your horse.