Have they continued to chew since the power cord? My parents' cat got a little too friendly with a power cord a year or two back and as far as I know hasn't gone near wires since.
I've used some inexpensive plastic wire loom to tidy up computer cables on the desk at home - this sort sort of stuff might slow them down, but if they're as tenacious at chewing on plastic as my cat is, it may not stop them. Heavier duty cord covers (like
these ) ought to keep the cables really safe, I would suspect. For the truly paranoid (or the really determined canine), you could even try surface raceway or wiremold - it would be less interesting to them than wire loom or bare cables, and like the cord covers would stand up to a lot more abuse if it did get gnawed on.
Want a really strange idea? It's one my dad used to keep squirrels off of tomatoes and I briefly used to keep them off the cable TV along the side of the house - a tabasco/hot sauce paste on the wires where they are exposed. The taste was a real turn-off to squirrels. Don't know if it would be similar for dogs.