I adopted a 13 year old brussels griffon/schnauzer mix who acts like he has never been on a leash a day in his life. The main problem is, he is deaf and blind. I would like to take him on small walks so he can get some exercise. I don't have a fenced yard, so I have to be really careful when I let him go out.
Thanks for your help.

Probably your best bet is a harness rather than a collar to attach the lead to. A halter collar would be my second choice.

Yea, a gentel leader would be a good choice as long as it didn't stress him out putting it on his face where he can't see what it is. Inormally wouldn't use a harness, but I think in your situation it might be a good choice as well.

Good on you for adopting.

At 13 years it's probably going to be difficult, but not impossible.

I would also suggest an alternative to a collar such as a harness.

The main problem I have found with harnesses is that the dog doesn't like the feeling around it's shoulder and behind it's legs but the good thing is the fact that you can put it on him and just let him walk around the house.
Try putting the harness on and giving treats, or even his proper meal (breakfast or dinner) just so he assiciates the harness with good things.

I was looking up training aids for deaf and blind dogs and came across this site: Paws to Adopt.

Unfortunately, the one bit of advice not up yet is leash training, however, it has some other interesting ideas that might help.

I don't really have much to add,but getting him used to the smell of it,his other senses are going to be super sensitive,touch and smell are going to be very important.

Your going to need lots of patience and lots of praise.

Another good thing to do is plant shrubs around the perimeter of your garden,something like lavender or strong smelling,once he gets used to the smell area of his patch he will be more confident.

And let him mark away in the garden.