When I was experimenting with my lasers I found a neat little trick to keep my lens protected. All you need is a finger condom, aka finger cot/finger protector. These work great for keeping dirt and other unwanted things from going into your lasers lens! If the laser is too big and the finger cot cannot be stretched over the laser, you can simply use one of those small bags that come when you buy small things off the internet. I hope this helps! Thanks for viewing.
Finger cots: http://tinyurl.com/hqp55of
Small plastic bags: http://tinyurl.com/hk2wqmu
Finger cots: http://tinyurl.com/hqp55of
Small plastic bags: http://tinyurl.com/hk2wqmu