[Mister Negative]

I experienced this as well. I love throwing weird animals/monsters at the PCs, and I disliked either option of 'the monster gets hurt with each parry' or 'the monster's attacks are all treated as weapons'.

I've tried two options.

One is allowing the damage as written, but specifying that the parrying defender cannot use his weapon to attack in his next turn (or, rather, he gets 1 less attack in his next turn). That way, he gets an automatic hit on a successful weapon parry, but doesn't get twice as many chances to do damage just because he's got a sword and the tiger doesn't. This was kind of fiddily in practice.

The other was to specify that you HAD to choose an Aggressive Parry in order to do damage this way. That made it work more the way I wanted it to work. People who were confident in their defenses, or who were fighting a less dangerous foe, might choose to do it, to wear down their inferior foe quickly. People who were facing off against really deadly attacks, or who weren't particularly good fighters themselves, didn't risk the -2.

I'm gearing up to run a DFRPG campaign in the next few months and I'm leaning towards using the second option again. It's more 'crunch' than standard DFRPG, but the penalty and reduced damage make it an option, rather than just a 'free shot' as written.

I also feel like you get the benefit, as an armed defender, of being able to target things like limbs (or heck, heads, vs. biters) without a penalty to hit in these cases, so you're already getting a pretty good deal, even with the -2.