There is always a risk that competition can play dirty tricks like that but Google has tools in place to monitor and prevent click fraud. They are referred to as "invalid clicks". You can run a report to see if there have been any invalid clicks caught on your account.
I'm afraid you can't. Google is filtering clicks that looks like click fraud (ofcours not as many as they should) but there is nothing you can do to stop it. What you can do is to claim refund from Google. If you have 3rd party tracking and you can provide reports with clicks,conversions,IP's, referrers, time/date - get that all together and send to you Google manager. If you don't have one, then you need to send it to general email. Sometimes a simple phone call to your competitor will do the job. Don't shout, be calm and explain them that it can work in both directions and on end of the day you both will be loosing money when others will get benefits from that. Good luck
U don't need to have much concern about invalid clicks by your competitors or any other resources. Adwords system has much sense to fight with such vulnerable activities. For much information on this topic i am pasting here URL of a video, i am sure it wud help u lot...... http://adwords.google.com/support/bin/answer.py?hl=en&answer=90448
I see every week I have invalid clicks but only ever get a refund every now and then from Google, never to the levels of these reported 'Invalid Clicks'. Last week I got 20, but did I get a refund for anywhere near that amount? Nope!
Track the IP's that hit your website. When you see a single IP that has come to your website say 10-20 times in a week add them to your IP exclusion list in Adwords. Google will not show your ads to them anymore. Tools -> IP Exclusion Cheshire
nothing you can do unfortunately - if it looks like your account is being taken advantage of then Google will probbaly do something about it. If you think it is and Google aren't doing anything then get hold of your logs and get in touch with Google with th evidence, they're usually very happy to sort that kind of stuff out
That hard to prevent competitor click your ad if they using proxy click your ad you can't know which IP come from .
Not only does Google do a great job at catching them, but if they click a lot and get away with it, guess what? Your CTR goes up, and your costs come down. They'll hurt you a little, but not a lot. And if you don't go away, they'll give up kinda quickly.
There is not much you can do as blocking IP's is only a minor fix. Also, by using proxies, or multiple locations not only can't you block them but Google will not recognize them as duplicate clicks. At the end of the day it's a cost of doing business. Write it off and move on.