Note: You will need +-50 slayer points.
Step 1: Click "Combat Training Teleport"

Step 2: Click "lvl 51-90: Death Plateau/Warriors Guild"

Step 3: When you get there, run south. You'll find a building. Enter it.
Step 4: When you enter, go through the Cyclops Portal.

Step 5: Talk to Kamfreena, she'll tell you this:

Step 6: Kill the cyclops' until you get the defender.