Look at the thread on page 2 titled "Ring Those Bells" by BubbaLeroy. There are pictures I put on the forum of the bells my husband made and mounted by the door. The only cost was for the bells from the hardware store and a L bracket. We had the jute rope.
Our new to us eight month old Basset, Bogie, learned to ring them in just a couple of days. We rang them every time we took him outside the first day, the second day we had him stand close enough that we could move his nose so he actually touched the bells and made them ring. The third day, I think I have the time line about right he did it on his own. Works great.