four balls in the pussy

If you've never put a pair of these "ben-wa" balls up in your wife/GF and fucked her (with them in), you're really missing out on an intense experience. Skip the ones (like these) that are connected. As long as you only put them in her pussy, they're not going anywhere, you won't need a string for her to "hatch" them back out.
Plus, they're probably the only sex-toy you can leave sitting out on your desk. Most people ignore them as "hand exercisers" but those who know... know. Go into a Chinese shop with your wife and buy a couple different sizes (hint: use the largest ones that she can fit) and see the smile on the clerk's face.