I have a strong field with many backlinks, which ranks first in a google keyword. If I rent my domain to a friend make a redirect for a year when I have him back, will remain strong and being in first place in the current keyword?
A domain with many backlinks, high strength and good position on google loses strength and position if redirected to another domain?
That's very tricky and might be a form of manipulation that could end up penalty for your site, 301 redirect is the recommendable redirect out there and it should be permanent. Just place a much noticeable link from your site to your friend's site..
Your redirect will pass a strong on authority and link to a domain you redirected to. It may not strong as it were when it's back. Google pay caution on redirect because of abused redirect usage in the past. 301 redirect is a safest solution but may not guarantee when you made a second redirect back to it. Some links which built during those period will give weights to a domain you redirected, yet not transfer back to a first domain when you made a second redirect anyway.
bad idea , that just wont work . after having it redirected for 1 year , you will pass the juice to your friends site and nothing is left for you
301 redirect is the best redirection way opted by the Google, when you redirect your domain to another then 301 shows a permanent redirection to the new location. But it can't be said when you would get back on the previous one, it would give you the same strength and ranking for the first position in Google. It may loose the previous strength as it was doing from last one year. So In my opinion, it would require time and efforts again to get back on the same position.
I'd recommend a permanent 301 redirection in your case... Make sure it is "permanent" or you get a penalty :_)