You see, there was this discussion about whether we are MudCats, MudKittens or MudWhatever...
Then I noticed there are some other members called Mudjack, MudPuppy, MudKat...
So the first part of my nickname had obviously to be Mud.

Now for the second part:
My (German) surname is Waechter, which translates into Guard.

I just put these two parts together resulting in MudGuard.
And some weeks later I learnt there is an English word mudguard (which translates back into German as Schutzblech).

MudGuard