He'd lure them in a steel cabin with food (probably raw human flesh), lock them inside with copious amounts of booze, and wait.

 

Wouldn't being under a silencing spell during a duel be a good thing? I mean, you are still saying the spell, the only difference is that no one knows what you're saying.

 

Not if your name is Dolohov, apparently.

 

No, you have to actually say it and say it correctly, unless you can cast silently. A good example of this is the DoM fight, where Dolohov's curse is weakend, because he can't cast it as well silently and Neville completely fails at casting, because his nose broke.

EDIT: God dammit, that post was there for three hours and I still get ninja'd.

 

Exactly. If you haven't extensively practiced casting without the spoken component, good luck doing so with comparable proficiency, when suddenly losing the ability to speak.

Unless it's a spell preventing others from hearing you, and you still fully believe (and perhaps perceive) that you are speaking... In that case, I'm reasonably sure and it makes some sense that, the magic would still work. It being at least a fair portion based upon will and intent, such that if you are making the right motions, perceiving yourself as verbalizing correctly, then it just might work.