Yesterday I mentioned the way you can stack DB up very high in DF. In RAW DF, you can potentially get 19 DB from your front arc, 13 for your shield side, and 5 from everywhere. Potentially higher with more than normal Magery. How?
Shield: Large Shield (DB 3), Deflect +5 = 8.
Armor: Deflect +5 = 8, and it's all-directional (not that you can defend from back shots, but this affects flank shots)
Shield spell: +6 DB (with Magery 6)
So with, say, Dodge 4 (3+maximal encumbrance), you'd have a 23 Dodge. 26 with Retreat. Seems fair, right? You can still fail on a 17 and critically fail on an 18, or be critically hit.
One thing I do, mostly to avoid the headache of needing to know where someone hit before you can calculate your defenses, is eliminate Deflect as an armor enchantment. Gone.
But I thought of a few ways deal with this:
Step 0: Remember the Rules
First, as written, DB is not passive. It's an addition to active attempts to defend yourself. It must be coupled with an Active Defense.
Second, a shield only covers your three front hex arcs and your shield side (and that at a -2). A Shield spell only covers your three front hex arcs.
Third, a higher DB shield gets hit more for purposes of Damage to Shields (p. B484) and Striking at Shields (Martial Arts, p. 112). That makes it both more likely to take damage from a direct hit and easier to hit on purpose.
Option 1: Limit Maximum DB
Cap DB at a given level; 8 DB is recommended (see below).
Notes: Simple option here. Why DB 8? The most you can get for a Deflect +5 large shield is DB 8, so just say the most you can get from all sources is 8. Have a large shield (DB 3) with Deflect +2 (total DB 5 now) and your buddy puts Shield +3 on you? You've hit the max. Exceeding the max is only useful to avoid the higher DB of your shield from causing it to get hit more by putting on a separate source of DB. You could set it lower, if you like - say, 6, matching Magery 6. High levels of Deflect only appear on very small shields, probably combined with metal construction and Shatterproof!
Option 2: All margin-of-DB defense rolls still suffer contact effects
When you make any defense only by the margin of your DB, your shield (magical Shield spell or whatever it is) takes the hit and you suffer knockback per p. B378
Also, since DB represents an impact, follow-up effects may be triggered normally. If a HE round hits the DB of your Shield spell, you may still suffer damage from the explosion and shrapnel. In short, treat magical DB as effectively infinite rigid DR - nothing that hits it can penetrate, but effects that follow on may still affect the target.
Notes: This may in fact be intended by the RAW; it also may not be. But either way, it means putting DB on yourself doesn't make it easier for you to slip an attack entirely, just not get hit squarely for damage. You might still get knocked back or down, or suffer from a fiery explosion or something like that. Note that this doesn't mean Cosmic (Ignores DR) attacks are also (Ignores DB), but a corrosive splash effect that comes with an attack, an explosion, etc. are still considered to have gone off in the same hex as the target. You're basically just saying all DB rolls are "Damage to Shields" but the shield has infinite DR, like a superscience force shield does, but that doesn't mean the flaming oil, etc. just disappears.
Option 3: Use the Highest DB Source
Instead of adding up DB, just choose the highest level of all of your sources.
Notes: Effectively this means the Shield spell is mostly useless for guys with good, magical shields. But maybe not - the shield is still there to Block, and if your large shield has DB 3 and you have Shield on you for 4 DB, you get a +4 to defenses and still get a Block, which someone without a shield does not get. You aren't stuck only with Dodge vs. missiles.
Chris Bower mentioned this one yesterday, so I took the idea and expanded on it a bit here.
Option 4: DB doesn't affect Close Combat
Treat all DB from shields, Deflect, etc. as a shield. It does not cause any penalties, but also no benefit, in close combat.
Notes: Like it says. Pretend it's a shield and suffers the "too close to use" effect.
Option 5: DB can only add +100% to Active Defenses
There is no limit on DB; however, your Active Defense + DB can never exceed (2 x Active Defense). For example, Alphonse has a DB 3 large shield with Deflect +2, and has Block 10 and Dodge 7. With DB, his Block is 15 and his Dodge is 12. If he is injured to half Move and Dodge, his Dodge is 4, so his shield can only bring that up to 8, not 9. Penalties apply after the cap is applied, so if Alphonse was on Bad Footing (-1 active defenses), he'd have a Dodge of 7. His shield would be hit squarely on a 4-7.
Notes: Do whatever you like, but you can only benefit if your skill or move is high enough to make use of your excess DB. You can be more generous and say the cap applies after modifiers, but that'll mean Stun (-4 active defenses) will have little or no effect given multiple DB sources.
You could stack a few of these, but they all have some nerfing effect on the Shield spell and Deflect enchantment. Only 1 and 3 - capping DB or taking the highest - merely say you can only go so far, so it wouldn't really affect anyone until they got silly. The last takes a little math, but it would mean your crazy DB only helps if you've got the underlying defenses to back it up.
Personally, I like the idea of 1 and 2, where there is a cap and you do still get whacked, but it bounces off your invisible force field (Shield spell) or your shield somehow gets in the way despite being too small (Deflect). It also nicely makes the Defending Shield enchantment worth a lot more than Deflect for Block because it is always uncapped.
I'll see if my players like any of these. It's not really a "nerf Dryst" thing, although it was his extremely effective defenses will mind-numbers, retching, and cornered by much bigger foes that partly triggered this thought. That fight made me think, well, how freaking ridiculous can it get? In my opinion, a little too ridiculous. So I'd like to try at least one of these.