Google and the other search engines have pretty good systems in place to detect and protect against clickfraud. They have billions of dollars invested into the reliability of their ad programs. I wouldn't be overly concerned but you should definitely use analytics tools to monitor your data. If you suspect clickfraud, definitely let the correct representatives know and they will investigate.. Google in particular has been very good at making reps more available to endusers even with lower adspend.
Click Fraud is much less of an issue today than it was a decade ago. These companies have too much too lose if the reliability of the ad system were compromised. They need to serve relevant ads to relevant searchers otherwise advertisers wont pay and the system would break.