[![enter image description here][1]][1]Using 2 command blocks, 1 comparator, 1 building block, 1 redstone torch. You can accomplish this thus:

 - Command Block 1: `testfor @e[r=radius, type=VillagerGolem]`
 - Command Block 2: `your command`

You will still need to put a clock on it. Mine is underneath the golem :)
  [1]: https://i.sstatic.net/Ehhna.png