Here is the Cryptsy EXE bid wall as of about an hour ago, using data from the Cryptsy order book http://pubapi.cryptsy.com/api.php?method=singleorderdata&marketid=183:

http://i.imgur.com/dv86UyK.png

Notice the nice wall being constructed at 3500 satoshi, with help from a step at 3650. The wall is about 40,000 EXE in height (1.4 BTC). My guess at the minimum height of a rock-solid wall capable of withstanding a modest assault would be at least 1% of the coin supply (5877450 EXE * 0.01 = 58,775 EXE or 2.06 BTC). A bomb-proof wall capable of withstanding a tsunami-scale attack would probably require 10% or 20 BTC. If we can get to 2 BTC, that would be a good start, and we're most of the way there already.

If we are successful with this campaign, the next question would be when and how much to move the wall. We could have an ongoing discussion and move the wall by consensus, or we could have a guideline that requires no further discussion. For example: "When the bid wall reaches X percent of the outstanding coin supply, advance the wall 100 satoshi. If the wall falls to X/2 due to an attack, retreat 100 satoshi." This formula automatically accounts for the steadily increasing coin supply, and requires no ongoing discussion unless the formula needs to be changed. If the chosen height X proves to be too small, we can double it.