1) The women might be having sex occasionally (when their husbands come home every few months), and this is what they are going to withhold. If a man hasn't gotten any for a long time, and is counting on finally getting it, withholding even once could be a very powerful tool.

2) Lysistrata says that the "deal" is big and hard. When she says "deal", does she mean the *problem* or the *solution*? The problem is war, and lack of penises. The solution is to withhold sex, also penisless.