I do not know the answer, but one thing I would suggest is to let ur dog know that it is unacceptable to chew on the wood of the deck.
Let them outside & watch them. As soon as they chew on the deck u can
a) make a loud growl noise & then calmly say 'dog is name' LEAVE IT' or
b) make a loud noise, like some coins in a can or something else loud, dogs r so sensitive to noise. Shake it & calmly say 'dogs name' LEAVE IT. or
c) u could say the same thing & then squirt the dog with a water pistol (if u dog hates water) or
d) say the same thing & shut dog in a very small bathroom for 10 minutes, immediately, or somewhere else that is unstimulating, & like a punishment
(I would not particularly recommend the water pistol because it makes dog is scared of baths, rivers, the sea, the hose, anything to do with water, but I have an extremely stubborn breed of dog & it was the only thing she would listen to)
good luck, soundsl ike u have ur work cut out for you, with 2 young pups, & those breeds will be wanting lots of exercise i'm sure.
Make sure u get good advice about dog training & do it now, before they form bad habits.
You do not want an out of control boxer/german shepherd & rottie!