Tracking banners from internal subdomain

I have the website: example.com which is displaying internal banners hosted on ads.example.com.

I've tried to implement utm tags to the destination URLs but that screws up my data because it overwrites the original source/medium/campaign attributes of the user.

So now开发者_StackOverflow I'm looking for a way to effectively monitor the impressions & clicks of these ads in analytics without overwriting the analytics cookies.

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Try using Event Tracking code its easy and good to track without manipulating your source medium data. Here is the sample code:

onClick="_gaq.push(['_trackEvent', 'banner-name', 'size', 'ad-content'])"