I found the the tutorial on Design*Sponge and went to Lowe's to buy my 5/8" thick sisal rope (about $0.59/ft). The video I found most useful, between the 3 listed on the tutorial, is this video. First note, if you decide on making one yourself, tip #1: wear pants. I had on some shorts, and when I was done my legs were red and itchy. It's abrasive on your skin, and tiny fibers get everywhere. Which brings me to tip #2: do it outside. Third note, I didn't add a tenis ball for the door stop and it is still heavy and works perfectly fine for us. It was really difficult for me to add it is, so I just left it out. I also thought making it really heavy could make the loop end from coming undone. Lastly, tip #3: applies only to dog owners with a dog who thinks the door stop is their new chew toy. Dogs hate spicey things. I made a shallow bowl of some cayenne pepper and water. Then poured it all over the knot. Left it outside to dry and tested it with my dog. One lick is all it took. Never touched it again. I love my dogs-but I also love my things to be intact.
Here it is on our door:
Feel free to PM me if you have any questions!