I'm going to get some stick here.....
When I was a lad I used to help the local farmers with lambing. Part of this was to castrate them. To do this a small rubber band was stretched over its bollocks and released. To do this a tool called an elastrator was used. It's either 3 or 4 prongs that open up with a small Ridge so the ring doesn't fly off.
I had to do the front ball joints on a vw transporter and I bought one of these tools to do the clips and it worked perfectly. I did think about electricians cable label stretchers too but the elastrator has a little groove.


http://m.ebay.co.uk/itm/ELASTRATOR-C...295?nav=SEARCH