Preventing ads from serving malware to visitors

It seems like all but the most premium ad networks/agencies/exchanges/whatever-places-that-provide-ad-tags-call-themselves inevitably allow ads that try to install malware onto visitors computers to slip through. If you're not a huge site, a few threads started by members about the malware they received from your site (the ads) and the resultant drop in traffic can be devastating.

How does everyone prevent malware from being served to their visitors via ads? Is it really the case that there are only a handful of ad networks you can actually trust not to inevitably serve malware, flashing ads, or ads featuring suggestive, scantily clad 16 year old girls to your visitors?

We've been trying to find a network to use for default/backup tags, but each time we try one things seem to go alright for a while until the community is up in arms about receiving a virus from the site, resulting in a loss of good will, traffic, more members blocking ads, etc. :(

How does everyone monetize their site beyond adsense safely?

Adsense is not only way of monetising. I can give you one example. I have abig webmaster forum. There i used banners to make money some time. When i hire these banners i ask like 100 amount cash. One day i decided to advertise my seo service at the same place as a banner. I made 8 times more revenue during the 1 month. You need to advertise your own products on right niche site. I dont sell hosting but one day if i do it'll be very huge for making cash. You can find what can be sold on their site and promote it.

Also you can make more money with CPA like clickbank products for sale or use adsense alternatives such as exitexchange, binlayer (popup) etc.

Furhermore adsense has a tool to check advertisement before they appear on your site. i am not sure if you know it. This is nice thing to use but takes time to manage.