Word association happens all the time; and when we think of the word 'steel,' we immediately associate it with being a strong force. Of course, that doesn't mean that plastic fences are weaker or a waste of money; it just means that they aren't a good fit for large dogs that chew and dig.
Plastic dog fences are strong enough for small or calm dogs; but for dogs that chew, it's best to buy metal dog fences with PVC-coating (Steel Hex or Welded Wire) that can stand up to a rambunctious dog that likes to play rough. The PVC is coated around the steel to prevent the fence from wearing down due to weather elements. It also protects the fence from the chew marks that the dog has set in the fence.
Fencing in dogs doesn't have to be hard work; but with the wrong fence in place, fixing the fence will take more time and cost more money.