#Tower Shields are always bad for a character

It is literally impossible to use a tower shield where you would not be better off using a heavy shield. See [my answer here](http://rpg.stackexchange.com/a/48555/4563) (and note that the accepted answer posits a single niche use-case that only “works” because of a misunderstanding of the rules). Only four classes gain proficiency in tower shields by default, and three are prestige classes that you aren’t using. The fourth, the fighter, has *myriad* options for replacing Tower Shield Proficiency with something else – which, by definition, is better.

Anyway, reducing ACP is fairly trivial; just have the shields made from mithral. The tower shield in *Player’s Handbook* is made of wood, but *Races of Stone* has a steel tower shield (which can then be swapped to a mithral tower shield), and *Races of the Wild* just has a mithral tower shield (which, oddly enough, appears to be the core tower shield, i.e. the wooden one, with the standard mithral modifiers applied to it).

Though I have no idea where you got the idea that having an Armor Check Penalty of greater than −1 prevents you from dual-wielding. That is not a rule. Armor Check Penalty doesn’t really apply to *anything* aside from the relevant skills, so long as you are proficient.

Being able to bash with a tower shield, though, that isn’t an option I’m aware of at all, feat or otherwise. Your reference to a third-party book (*Plot and Poison*) may indicate broader allowed material than I am familiar with, but I am about 90% sure that Wizards of the Coast never offered the option. Even if they did, again, ***tower shields are bad for you.***

#Dual-shields, on the other hand, is quite effective

I have run a couple of dual-shield characters, and both were quite effective. They both used a heavy shield as main-hand and light shield as offhand weapon, which is almost-certainly the most effective way to go about it. Dual-shield is a quite feat-intensive build, and wasting additional feats on allowing you to competently use two one-handed weapons is not a good idea.