It is my understanding that Magus cannot use Metamagic Rods in conjunction with Spell Combat or Spellstrike (since you have to have the rod in hand to use it, but you have to have a free hand to use Spell Combat, etc.) so you can't cast a spell with a free hand AND hold the rod AND wield your weapon at the same time.
However, could you wield the Rod as an improvised mace in your "main" hand? That would seem to meet all the requirements of having a free hand, wielding a "weapon" in the other hand, and having the Rod available.
If the Magus in question was a Kensai, that wouldn't work though. Would it be possible to make a Ring, or Bracer, or other item function as a Metamagic Rod? Would you price it the same? Rods don't take up body slots, but a Ring, or Bracer would. Would that change the pricing at all? Would the crafter of such an item need Craft Rod AND Forge Ring (or Craft Wondrous)? I would think so.
You could use a weapon that doesn't take up a hand, such as a boot blade or Dwarven boulder helmet.
You could always dip into alchemist for an extra arm or something. Magus have it difficult when it comes to rods.
Were I your GM, I'd let you go ahead and make, or even find, a metamagic rod that was an actual light mace. After all, lots of rods are also light maces. But I've been accused of being lenient.
Be a Tiefling and get the Prehensile tail variant to hold your rod.
Vanara and possibly other races also have tails, but Tiefling is the best race for a dex magus already anyway, so it's the preferred choice.
I also think whether using a metamagic rod actually requires it to be held or not is disputable and the text contradicts itself. But considering it was changed from "absolutely don't have to hold it, just possess it" in 3E to "could go either way...", I assume the intent in PF was to make it need to be held.
I also think whether using a metamagic rod actually requires it to be held or not is disputable and the text contradicts itself.
Can you post the contradiction you're talking about? I was trying to find it, but my eyes did the gloss-over thing while looking through the rules. It'd be a big help so I could understand what you mean. Thanks.
Here is the rule for activation, from the rod entry:
Activation: Details relating to rod use vary from item to item. Unless noted otherwise, you must be holding a rod to use its abilities . See the individual descriptions for specifics.
And here are the rules for metamagic rods specifically:
Metamagic rods hold the essence of a metamagic feat, allowing the user to apply metamagic effects to spells (but not spell-like abilities ) as they are cast. This does not change the spell slot of the altered spell. All the rods described here are use-activated (but casting spells in a threatened area still draws an attack of opportunity). A caster may only use one metamagic rod on any given spell, but it is permissible to combine a rod with metamagic feats possessed by the rod's wielder. In this case, only the feats possessed by the wielder adjust the spell slot of the spell being cast.
Possession of a metamagic rod does not confer the associated feat on the owner, only the ability to use the given feat a specified number of times per day. A sorcerer still must take a full-round action when using a metamagic rod, just as if using a metamagic feat he possesses (except for quicken metamagic rods, which can be used as a swift action).
It says Possession allows you to use the metamagic feat. Not holding the rod. Arguably, this counts as triggering the "unless noted otherwise..." clause.
The reason for this mix-up is that in 3E, specific rods said if you needed to hold them to use them. Metamagic rods did not say you needed to hold them. PF added a general rule for all rods that you need to hold them unless it says otherwise, basically the complete reverse of how 3E handled it.
PF then basically copy-pasted the 3E metamagic rod text verbatim (they did change/add the part about sorceror and quicken rods, since in 3E a sorc / any spontaneous caster could not use quicken spell in either feat or rod form, but in PF he can), leaving the text bolded above that confuses the issue.
Again, needing it in hand is probably the intent due to the fact they attempted to change things at all, but RAW is unclear. And specific rules tend to trump general rules.
Fair enough, though I'd say the word "wielder" in the description of the individual metamagic rods implies that you have to hold it. The 3.5 descriptions of metamagic rods just said "You can", not "The wielder can", and all other situations in which they refer to a "wielder" or "wielding" it means that you have to have it out and at the ready. Just my thoughts on the matter, of course.