The blind retreive is a matter of trust between the dog and the handler. The blind retreive is especially useful for tracking, go-backs, frisbee/ball catching, and directed jumping.
a number of wooden dowels (the size of the center of your retreival dumbell) - usually about 5-7
A large space (about 100 feet)
Lots of treats
Step1
Teach your dog to retreive the dowel. Meanwhile, establish your dog's visibility limit (how far can the see distinctly?). This is usually done by putting the dowel further and further away from the dog and see the limit of where they go directly to it.
Step2
Place two dowels out, one just short of normal retreiving distance, and the second half that distance beyond it. Send the dog for the first dowel. Upon a successful retreival, re-line up the dog immediately and send them for the second dowel. Most dogs at this point will react in confusion (hey, wait. they didn't set out another object - I would've seen it). If the dog refuses the retreive, direct them to the dowel - even if it means walking the dog all the way and pointing to the dowel. Repeat this step until the dog retreives two dowels in succession.
Step3
Now the building process begins. Add more and more dowels, each 1/2 to full retreival distance beyond the previous dowel. What you are teaching the dog is that, "If I send you for an object, trust me - it's there. You just need to find it".
Tips & Warnings
Don't worry if the dog leap-frogs over a dowel (retreives the one beyond it). Reward the retreive and re-send.
Always line up and send the dog distinctly for each retreival.
Since this is going to be used for go-backs and directed jumping, you may want to use a different retreival command. Some people use "Run" or "Go". I've always preferred the football terminology of "Go Deep" or "Go Long".
NEVER SEND THE DOG IF THERE IS NO DOWEL. Don't lose count. Nothing will undermine the entire trust-building exercise like not finding the dowel.
Always reward the retreival.
Do not allow the dog to drop the dowel and go after the next one by themselves. Each retreival needs to be commanded.