I have been married for 18 years and (most, <laugh> ) of those my wife and I have had a wonderful sex life. When we were first married I did have a problem with "doggie-style" and did pop-out a few times. It's all about getting used to your partner and yourself as well.
The key is trusting your partner. If that happens to be your wife, then you two should trust each other enough that something silly like popping out which might be embarrasing for you, might turn out to be a funny moment that the two of you can share. I hope that helps!
I am an inch shorter than you are. It is true that at times in some positions, ie doggie, it pops out. Like the previous post says, learn to live with it. In missionary position, I can maintain a hug and pull it out. I do this to my wife at times and instead of reinserting, I run it up over her clitoris a few times and back in. This gives her a thrill. There are other advantages of having a small one. It does not require as much careful stretching to do anal sex. I do confess that like many of us who have short ones, I have looked at the long ones with envy, but I am happiest when I realize that this is the way I was made, and start learning the best techiques for a shortie!
Hey bud, tomtink is exactly right! Size doesn't matter even if we pop out, its all about your partner and the two of you working together! I know, I'm just a bit bigger than you and often wandered the same thing until I got married and discovered things were just fine!