[The_Gun_Nut]

Which really upsets mages, as they had to burn lots of karma to get that focus.

That'll learn ya to keep 'em on all the time.

[Darkeus]

Hmm, why do they hide these things!!   I must have missed that when I was reading. 

Oh joy, I got another thing mages in my game can spend money on again!!   

[The_Gun_Nut]

And karma.

Don't forget the karma.

[Darkeus]

And karma.

Don't forget the karma.

Oh I never forget the karma....   

[Magus]

Astral Tracking
Nearly all magical things (spirits, spells, foci, and magical lodges) have an astral link to something. Active spells are linked to their casters, spirits are linked to their masters, astrally projecting magicians are linked to their physical bodies, and foci and magical lodges are linked to the magicians who activated them. Awakened entities who are aware of these links can follow them and track them through the astral plane back to their sources.

And a few pages earlier:

Spells cast on astral objects like mana barriers or active foci are resisted with Force.

So you can target an active foci on the magic-user, grounding the area affect on the foci. The foci then resists the spell as well as everyone else in the area of effect. It doesn't make it easier to hit the mage, and he might still survive, but with the right spell, you could take out a focus as well as the mage.

But only if they are dual nature at the time. And you can only cast a Mana Spell on the Astral. So technically it is not Grounding in the Second Edition sense. That was thrown out in 3rd ed. Plus it does not destroy the Focus it only deactivates it from the astral.