Before you begin teaching your blind and deaf dog to "stay," it's a good idea to already have a reliable "sit" or "down." Also, start by working in a low-distraction environment, like at home.
Step 1: Choose a command. I like to use a flat hand on the nose.
Step 2: With your dog in a "sit" or "down," give the new "stay" command, and wait a short amount of time (less than a second, to begin with), and then reward.
Step 3: After rewarding the "stay," give your dog a release command, and encourage him to move. I run a flat hand over the head towards the nose.
Step 4: Add duration by slowly increasing how long your dog must wait before being rewarded. If he breaks his stay, move him back to where he was, give the command, and lesson the amount of time he is required to wait.
Step 5: Once your dog has a reliable stay in low distraction environments, you can start to add distractions, and different smells to help proof the command.
Remember to keep these sessions short - even just a few minutes at a time, to keep things interesting for the dog. Always end sessions on a high note, and set your dog up to succeed. If you find yourself, or your dog getting frustrated, take a break and try again later.
While these methods have worked for us, it is important to remember that every dog is different and what works for one, may not work for another.