I've had a couple of clients who've been living under, what I consider to be, an illusion that buying different domains with similar keywords and redirecting them to their main site will be somehow beneficial to search results. Say if they own homedogtrainer.com but also want to target teaching dogs tricks they register teachingdogsticks.com and simply redirect it to their main site homedogtrainer.com. I'm not sure where they're getting the idea from? If there's no links anywhere to the second domain there's no way for search engines to even know it exists, but even if there was would it make much of a difference? Personally I'm always going to recommend that the exercise is pointless, but I wondered if anyone disagreed with me?
the way to do it is to create contents rich pages targeting the relevant KWs on the "new" domains/sites and then link form them to the main site. Simply redirecting the domains will not work.
There is a way for the second domain to be known by search engines if you don't point any links to it. All webhosts have some sort of file register that lists all the sites that are with that website host, and the links are hyperlinks which are also followed. Plus some hosts ping search engines when the account is set up.
That may have some very tiny effect, but this isn't a website I'm talking about, there's no hosting involved, it's just a domain name redirect.
The only way they would benefit is if the domains were getting type-in traffic relevant to the site being redirected to.
It is pointless to get domains for redirection purposes. The best thing to do is to give them good contents with links to the site(s) you are promoting.
Teach them the benefits of landing pages for specific keywords. it's also a killer way to build their email list as well. see if they would like to have separate domains with landing pages that provide information, collect an email, and LINK back to the preferred website. PM me if you have any questions.