Do you strap them to the front or the rear of the fan? Doesn't having them on the front (i.e. where the air blows out) mean that the fan will get dirty since it's sucking the air in?
You may wish to use a cheap thin washable pre-filter either way. It will catch a lot of the hair before it hits the fine filtration, which you can then just wash off the pre-filter, making it easier and cheaper to maintain.