I'd say 2 things

If you are dealing with "take out dog BEFORE he knows you're there" - look up the term "Hush Puppy" - a nice Ruger MkII with a supressor

For dog packs, the summer I spent at my cousins farm in Canada, we had a LARGE problem with a ferral dog pack (there was about 75-80 dogs in the pack). We found a Lee-Enfield in .303 worked wonders. One afternoon we saw the pack, and trimmed out about 20 dogs before they ran - they were not sure where we were (Hint - up in the bucket of a payloader - about 200 yds out. Pick the biggest dog, shoot, repeat)