RAW, I'm with Fortinbras, but only in relation to Direct Combat spells (eg Powerbolt). Standard rules do not allow physical objects to get Counterspelling assistance to defend/resist this limited list of spells.
RAW, physical objects do get resistance rolls to other physical spells (Indirect combat spells, levitation etc), so Counterspelling should apply there normally.
However, I think it's quite reasonable for a mage to dedicate counterspelling to a physical object from Direct Combat spells, so in our campaigns we House-ruled to allow Counterspelling dice (only, no attribute) to assist in resisting Direct combat spells as well.
Note: We included limitations on the size of objects that could be counterspelled, though. namely:
- Must be a wholly contained physical object with body (or structure) of (Magic x 2) or less.
Again, this is a house rule, and RAW is not really required. Seeing as only Full Magicians and Mystic adepts get access to counterspelling, this has only been utilised maybe three times in a year of campaigning, so it's not a big deal either way.