Can I put this on a 6 ft fence in backyard? How tall is it?

Depends on whether you are using the entire width of the screen on your fence. It is about 5 feet tall but more than 8 feet in width (16:9 ratio). If you meant 6′ high it will fit. If you meant 6′ wide you will have screen to spare assuming the fence is 5′ high or higher.

Make sure you have a good hanging solution on order not to damage it. Try using double sided Velcro.

For more information please check out our guide setting up a great backyard setup
http://outdoormoviehq.com/ultimate-guide-to-outdoor-movies
Or take a look at our recommended projectors and screens
http://outdoormoviehq.com/outdoor-movie-screens