That's an excellent question because it also speaks to the timing of the sanctions. In order for sanctions to be unpredictable, they have to happen quite quickly so as to take the other side by surprise.
Something I've thought about—I haven't seen it implemented anywhere—is whether there could be a consultative body composed of the government and parliamentary representatives of all factions in a given Parliament. They would form the authoritative body that would have to approve sanctions that could then be imposed swiftly.
I don't think such a body should have the right to veto sanctions, but it should be involved so that sanctions, especially very swift ones, don't come as a surprise to it. This matters, especially when the issue is one of sanctioning people who are not involved in the aggressive action we are trying to deter or punish, such as children of officials. However, if there is a consultative body, an advisory body, involving both the government and Parliament, I feel that would give some scrutiny and legitimacy to such decisions.