I'm pretty sure I've mentioned before that I think dogs would work best as a passive base defense, somewhat comparable to the Gap Generator; have a Kennel in the base somewhere that spawns dogs periodically to roam around the base, destroy the Kennel(s) to prevent dogs respawning. Maybe have the dogs put an indicator (like the arrows over cloaked units near an MSA in IA,) over the heads of nearby (15-20m from a dog, maybe?) spies, or even just any nearby Allied infantry unit, to encourage people working *with* the dogs to defend the base.
Preferably, the dogs would still be vulnerable to full-sized weapons, but for their anti-infiltrator role, having them be resistant to handguns (and thus, Spy, Thief, Engineer and Tanya) might be a good idea.
Though I must also admit, GeneralCamo's purchaseable buddy dog is also a good idea.