once again - banners here lasts much more than 1-2 year. maybe you have stronger UV radiation?
Banner over road - was hanging whole 3 years, before wind tear it apart.
Banner on fence - im changing price stickers on it for fourth year now. and it look like it will last for few years. But it shows fading by now.
One other banner - laminated - hangs for 1 year now and it is like new one.
The firm that welds banners even has a mashine for liquid lamination. It is the size of the large printer, and it applys lamination on banners...
So, here in EU banner lamination is often process i guess...