backorders almost never ever work, especially if the domain has any value. First off if the domain is somewhere like GoDaddy, even if you have a back order with GoDaddy, it will first go to their auction system before actually expiring. This means a back order on a domain owned by GoDaddy is pretty pointless since you could buy it at auction for less.

If you really want to get a name when it expires you have to use Snapnames, they work with tons of different companies to make sure you get the name. I did this recently and it worked out great (although you end up with a domain registered at some crazy company half the time and have to transfer it 90 days later)