Any tips for aligning fenders? I recently bought a used trekking bike (Focus) to commute to work in Berlin. 

It's a great bike, and now that the weather is a little wetter I'm finding that the fenders it came with aren't quite covering the wheels like I would like. About every two weeks they come out of alignment and I have to adjust the screws/bend the stays to get it to cover the wheel again.

Any tips for getting them to stay put? I've adjusted them three times now and it's getting old. 



EDIT: I'm not sure the exact brand/model but the rear has 1/2 diameter coverage and the front has about 1/3 diameter coverage. 

Material: black plastic

Attachment system: like these:


Or these Planet Bike ones:
I think the first step would be to work out what is causing them to fall out of alignment. Possibilities include:


Vibration when riding causing fitting screws to loosen or parts to rotate
Leaning your bike against something when parked
Someone leaning their bike against yours or tampering with them


In case 1, you can remove the screws and refit them with some threadlocker (a weak glue that keeps machine screws/nuts in place, usually blue in bike applications).

In cases 2 and 3, the stays may be getting bent or fastenings rotated, in which case all you can do it be careful how you park the bike and where you leave it.