Like the topic says, there seems to be a lot of cards that cause you to discard, and a lot of them see/have seen play over the years, but exactly what is there to avoid it? Counters(which could be used on better spells), Anti-targetting (which usually doesn't come cheap*)...
As for specific cards geared against being discarded or gain benefits for being discarded, we have... Dodecapod.

Going through the colors, I kinda figured out that White was the color of protection (in all of .5 seconds). After I decided on the color, all the while being kinda tweaked out at about 11:30 last night, I scribbled this down...
Payback's a Bitch
WWW
Enchantment
During your upkeep, pay WW or destroy ~this~.
If a spell or ability an opponent controls causes you to discard ~this~ from your hand, put it into play instead of putting it into your graveyard.
If a spell or ability an opponent controls causes you to discard from your hand, your opponent must discard an equal number of cards from their hand.
Looking back on it with a clearer head (and a bit of a hangover

), I see now that I was kinda inspired by
this Magi-Nation card and
this Yugioh card. But hey, that's not a bad thing, is it?
As far as I can remember, the upkeep is there so non-white decks do get one use out of it, but then lose it. Yeah, it seems kinda narrow, but Serum Powder's narrow as well, and that's going to print, so meh. Besides, I figured that it would be somewhat useful considering that nearly every deck I see here splashes Black for Duress.
Anyway, think of it what you will, and post away.