Kieren doesn't sound averse to the idea at first, asking after what spell Sirius might cast. And, truth is, he isn't certain right in that moment. He knows there must be something, however, something he can make perhaps with Kell's help that will create a sort of bubble of protection around Kieren when activated. It can't be something anyone can see, nor something he's required to wear. But surely he can manipulate a warding charm somehow. It can't be that difficult.

It's when Kieren puts up a bit of protest that Sirius snaps a bit, whirling around to face him, his eyes wide. "Yes, Kieren, you're a man! You're human. You're Muggle. And this city is full of magical creatures who can hurt or kill you just as easily as every other person. Whether you're grown or not has nothing to do with it! I'll not have you torn to pieces by-- by some wild animal or hungry vampire or ordinary human with a gun. There must be something."