Brine rats, which can drop the Brine sabre worth at a rate of 1/512, are found inside their cavern and require 47 Slayer and completion of Olaf's Quest. Using Fairy ring code is strongly recommended as it takes you south-west of the access point on top of the icy mountain where a spade is used to dig next to the windswept tree on the hill. Once inside, head east, then north and west in the cave. Collect the death runes, noted sharks and lobsters they drop. Also, at 45 Cooking, players can camp here by cooking raw swordfish using Olaf Hradson's fire outside.
This guide assumes 150 kills per hour. Your profit per hour may vary depending on your speed.