The first step in countering snipers is for everyone to be aware of the threat. This is where a threat assessment needs to be compiled and the realist threats need to be identified, if potential snipers are a threat then procedures need to be put in place.
In general, operational planning for a sniper threat should always be considered to some extent. Not only should counter sniper procedures be planned for but they need to be practiced, your people need to be trained at least in the basic reactions to fire and the use of cover, preferably before they are exposed to the sniper threat.