Travis Decker‘s not some unstoppable rugged action hero, according to the Chelan County Sheriff … ‘cause it’s the terrain — not his military training — that’s helping him avoid capture.

Chelan County Sheriff Mike Morrison tells TMZ … the Washington state resident accused of killing his three daughters doesn’t have any more training than the law enforcement officers trying to track him down in the mountain region of the U.S.-Canada border.

Sheriff Morrison says Decker isn’t “anything special” … arguing that even though he has a military background, the lawmen on the other side have just as much, if not more training. He adds they’ve also given more for their country.

Sheriff Morrison isn’t saying it’ll take that long to catch Decker … ‘cause Decker will have to be perfect every day to avoid law enforcement — while they only have to get lucky one time to slap the cuffs on him.

Decker — who cops believe was spotted just days ago in the Wenatchee Mountains — is receiving international attention during this manhunt … with law enforcement receiving several hundred tips from all over the U.S. — and even getting one from Scotland!

As always, Morrison tells area residents to remember Decker is out there and to stay on guard … encouraging them to call in a tip if they see anything suspicious.