Thank you for your responses. DaOld Man's parking brake is exactly what I was thinking. But i couldn't think of a good way to word that to google. The energized to release state is definitely what I had thought in mind. I considered a gear box because speed isn't TOO big of an issue with what I am working on, but if my motor stop half way through a rotation, it will have about 17 pound of weight sitting on it at an angle. I just figured this weight would be enough to engage the gear, and that is why I didn't look to far into it. Then with the servo idea, i liked it, but they usually cant sustain alot of weight, and I would constantly worry if it was in an "always-on" state.
lilshawn, the electric wheelchair set up sounds like you and DaOld Man were on the same page, and I think thats the best way to go. Energized lock release, but I would need it on a smaller scale. Connecting the motor leads was also an option, but like you said, they arent strong and if I am getting near 20 pounds, i doubt it would sustain. Lastly, the rotary encoder falls into the "always-on" scenerio.
Just so you guys know I didn't just blindly ask without wanting to do work myself, from the options I saw I thought a worm gear would be good. But between the lubrication and the surety that they can't reverse without adding more components, I thought maybe it wasn't the best solution. Thank you again for your guys' inputs.