Ach, that's a bastard... I've had one about the same length of time and although I've made the odd cock up over the years trimming it myself I've never gone to a barber with it. Don't think I ever will now...
The worst self inflicted beard damage I did was started to trim it without attaching a clip (I use a number 6 on it when I do to get an idea of the contrast) - had a little cut out shelf in my beard until it finally few out