Thread a doubled up arm's length of yarn through the eye of the locker hook. This is now the "locking medium." Many instructions online say to use cotton twine or an inexpensive yarn as the locking medium. I choose to use a doubled up length of the rug yarn so it would be thick and soft to walk on and when it comes time to tuck in all the tail pieces it is easier to hide them into the loops of the rug.
The yarn I chose for this project is a multi-colored gradient blend. So I used separate skeins of yarn for my locking medium and pulled the loops constantly from one skein. You can pull loops until the skein is completely used without having to cut the yarn at all. This cuts down the number of tails to be tucked in at the end and with a gradient blend the striping comes out nice and smooth. (see the final pictures)
It is best to use only an arm's length of yarn for the the locking medium because 1) it is faster and easier to pull lots of smaller lengths and 2) the yarn tends to get pulled and pilled up if it is too long and pulled through too many loops. I suggest varying the lengths of yarn for the hooking medium by a few inches so the end tails do not all fall within a straight line on your rug because if they do it may tend to make the rug look like there is a road bump running down where all the tails are tucked in. I used a heavily textured yarn which also helps to hide the tails and the rug has more of a bouclé texture to it.
Now to hook:
The rug yarn will be fed up from under the canvas and the locking medium will be on top.
Use the hook end of the needle to pull a few inches of the end of the rug yarn through to the top of the canvas. This is your first tail.
Insert the hook into the next hole and hook the rug yarn and pull back through. Keep the yarn on the needle shaft and make the loop about 1/4". Then inset the hook into the next hole and hook the rug yarn again and pull another loop up through and onto the needle shaft.
Once you have a few loops onto your needle pull the locking medium through the loops while holding onto the tails of the locking yarn. Now you will have 3 tails at the same place to be tucked in later. Always hold these tails when pulling the needle so you don't pull the locking yarn all the way out of the loops.
Depending on the thickness of the material you chose for your rug you can hook anywhere from 4 to 8 loops onto the locker hook needle before pulling the locking medium through. When you reach the end of the row rotate your canvas around and continue hooking loops on the next row.
The corners where four layers of canvas overlapped is not too difficult but it was tight so I worked it 2 loops at a time.
When you reach the end of your locking medium leave enough of a tail to be tucked in later.
After the canvas has been completely hooked go back and tuck all the tails in. Tuck all the tails into the loops on the top of the rug this keeps the underside of the rug nice and smooth (if the rug is to be used on a wood or tile floor add rug backing
for safety). Many instructions online use the locker hook needle to tuck the tails in but I think it is too thick and may pull your loops askew. I recommend using the tapestry needle and pulling the tails into rows next to them in the opposite direction the rest of the locking medium was being pulled. Snip off any excess tails that haven't been tucked in.
Here is a short video showing a few loops being hooked and the tails being tucked in:
Tip: The rug I made was 57" long and the canvas was stiff and difficult to work with (at first). I rolled up the ends of the canvas and used a few jumbo binder clips to hold the rolls so I had a smaller area to work with and I could hold it all in my lap while hooking.