Yes, we can stop them, but that will not be an easy task. We cannot just target the individuals, potential "lone wolves", because for every one we stop, there will be new one trying to accomplish what previous one failed to do. What we must do is eliminate the reason for their actions, by ending wars and instability in the Middle East. And that is the true challenge .
The problem with a lot of big-government thinking in Washington is that if we just throw more money at the problem, it can be solved. However, this is simply not true at a micro level. If somebody wants to break into your house or your car, they can. If somebody wants to shoot up a food court, it's almost impossible to stop them, without resorting to draconian tactics that would make me think the terrorists have already won.
A suicide bomber in Germany pledged loyalty to ISIS. There is no way to stop "lone wolves" because, without advanced intelligence, there is no possible way to effectively combat this. There are simply too many people and not enough law enforcement. This is a problem that will remain with us for a long time.
Unfortunately lone wolves will always be a problem. There are measures we can use to take to reduce the number of them, but we we will never be able to stop them altogether. Some of the measures are also more harmful than good as they will hurt people who are geniuses as well.