I've been meaning to post this for a long ass time (since it first
came in, in fact), but I kept procrastinating it and it wasn't until
a long ICQ discussion that I got off my ass and did it.

Deshield's overpowered. From what I remember of its implementation,
someone on the forums suggested it, and it came in shortly thereafter.
The problem is that I'm not sure anybody realized just
how massive a change it made to invokers. Clearly they weren't
underpowered before, and they received deshield without any kind of
compensatory toning down.

Having played the eternally persisting Dakizar, who was both pre and
post deshield, I got the opportunity to see the change in a fairly
controlled environment - before and after it came in - and it was a huge
difference. There are two issues with deshield:
1) Invokers can always have a fresh shield up
- This is fairly self-obvious. More than once I got jacked and
would have died, except that I had wisely deshielded and reshielded
and my shield therefore outlasted the blackjack. The counter is that
in theory, you're vulnerable when you deshield before you reshield,
but I never once got hit when I was like that, because it's damned
easy to avoid.
2) Invokers can too easily switch shields
- This one's a little more subtle, but I think it's more important.
The problem is, pre-deshield invokers had to pick one and stick with
it for the next 8 ticks or so. This made picking them somewhat of
a strategic choice: you could pick the one that minimized the danger
of thieves, but then you'd be screwed if you ran into that mace user
in the next 7 ticks. Now you just default to the thief/assassin one
and switch if you run into anybody else. End result is that invokers
are much less susceptible to thieves and assassins because there's
virtually no drawback to choosing that shield and always sticking
with it. Remember when invokers feared thieves because of trip?
Yeah, those were the days. The other end result is that invokers
get caught with the wrong shield much, much less.

I have more reasoning, but I'm too lazy to go on. Hopefully the
general idea gets across. Now, what do I think should be done short
of just scrapping the command?

Two things come to mind as possible and easy solutions:
1) Deshield timer - can't use it again for some amount of time, say 2 * length of shield
2) Deshield doesn't remove a shield, but sets its duration to 1

I'm sure there's lots of other options. Anyway, I've been meaning
to say that for a while. :P