As [mentioned before][1] there are [commercial products][2] available to solve this problem:

![enter image description here][3]

But that would be expensive and wouldn't be a proper life hack.

To save a little money you could just re-purpose an old pair of suspenders, you should be able to find them in thrift stores, provided you don't have a significant hipster population in your area...

![enter image description here][4] 

With this style of suspenders you can carefully remove the stitching, to separate the two elastic strips. Then you will have two working sock/shirt garters for around $2.


  [1]: http://lifehacks.stackexchange.com/a/1587/32
  [2]: http://www.shirtstay.com/
  [3]: https://i.sstatic.net/T3PSO.jpg
  [4]: https://i.sstatic.net/Z50qw.jpg