How can we keep aircraft safe from future drone strikes?

As British Airways flight BA727 from Geneva approached the runway at London's Heathrow airport on Sunday, something unexpectedly hit the front of the plane. On board were 132 passengers and five crew. Thankfully, the aircraft was not damaged and landed safely. But a police investigation has been launched and, if the object is confirmed as a drone, it will be the first known collision of its kind in the UK. What can be done to stop this happening again?