I'm helping someone whose website has a couple of domains pointing to it. Its been set up this way for years, but now they want to standardise on 1 domain. They will continue to direct the other URLs to that site, but they want to make sure that the standard domain always shows up in the search results. For example, they have www.domain.com and www.domainonline.com. They want to standardise on the shorter URL, www.domain.com. Unfortunately, there are links to both domains from other websites and the longer version is more likely to show up in Google. I've tried redressing this by getting some linking sites to change the link, but it's not possible or practical to do this for every site linking back. Any suggestions for how to tip the search engines in favour of the shorter domain?
Put up an htaccess file to 301(permanent) redirect the links pointing to domainonline.com to domain.com. There are many threads on that already in DP. Search for that.