Once you have Horatio in your roster, get at least 15 kills with him to unlock his Pig's Endurance skill allowing him to revive himself. Get yourself the Tactical Binoculars perk & a decent sniper rifle in case you need to finish off any stragglers & you're set. Stay outside the outpost and tag as many enemies as you can then send Horatio in to attack one of them. He'll draw plenty of aggro so once he's killed one guard just set him on another and let him do his thing. Seeing him will not cause the guards to activate any alarms as long as you stay hidden & you'll easily get the Undetected bonus. I've used this on every outpost & 9 times out of 10 I haven't had to fire a single shot.