Your only option is to come to Geneva International Airport by private car? Geneva Airport can provide a guarantee that you will find a parking space when you arrive.
As of 3 November 2009, the ResaPark service allows you to book a parking space over the Internet, at least 24 hours in advance. The service costs CHF 20, a one-off payment in addition to the usual cost of using the P1 car park. Travellers must pay the booking fee by credit card when booking over the Internet. The parking fee is paid directly at the Airport payment counters on you return. The 200 or so spaces available through the ResaPark service are on level -2 of the P1 car park.
Airport Management is pleased to offer this service to those passengers who have no alternative but to drive to GVA. It would however remind all other users of the Airport that they can get to Geneva International Airport by means of transport other than private car, particularly by using public transport (buses, trains, etc.) or the various shuttle services.