On entry to Camp Guardian you will receive a radio broadcast. Listen to it to receive word of Halford's problems.
There will be 3-4 radscorpions on the mountain path and several giant rats near the camp itself. After finding Halford's tent there should be a journal piece nearby telling the Courier of the cave behind their tent. On entrance there is a crate with several C-4 plastic explosive and a 9mm pistol. No lakelurks should be found on the way to Halford.
Upon finding him you will notice a blood pile near his leg. Having a doctor's bag or medicine skill of 50 will allow you to heal his leg. You will probably not have to fight your way out if you backtrack your path. Upon exiting he will give you his rifle in full condition and a note with schematics for the dog tag fist. He will tell you to take the note to his superiors.
The Camp Guardian distress call has no set order of messages, which means you could hear the same thing two or three times in a row.
If you kill all lakelurks and collect all four dogtags first, then talk with Halford, he will thank you, but there will be no opportunity to heal his leg and he will stay in the cave indefinitely.