The cages needs to be staked to prevent them from tipping as the plant grows. If they are not properly staked, they will topple when there is heavy rain or wind. You can stake them using wooden stakes driven all the way to the ground. Tie the cage into the top part of the stakes using long plastic ties or hemp. Optionally you can also use four rebars about 4 ft in length. You can place these rabars uniformly around the cage. Then drive them into the ground using a hammer to a deapth of about 1.5 to 2 ft. Then you can raise the cage to about 6 inches above the ground and tie it to the rebars at several locations.

There is a specific advantage in using the rebars to elevate the tomato cages from the ground. Since the cages are elevated, they will not corrode easily. Also it will be easy for you to do weeding and add fertilizer.

And finally here is the finished picture. If you look closely you will see the rebars at the bottom.
Advantages of wire mesh tomato cages:

1.  Saves you time

Tomato plants supported by wire mesh cages require considerably less work compared to either staked or trellised tomatoes. The plants are supported and contained within the cage. Ocasionally, you may need to guide a wayward branch back to the cage and that is it. Compare this to the constant tying and supporting necessary if you use a stake or trellis based solution. Before using the wire mesh cages I used to spend hours tying my tomato plants to their supports. But not any more.

2.  Saves you money in the long run  

Since these cages last for 10 to 15 years or more, your investment will last for several seasons.

3.  More tomatoes to pick  

They produce more tomatoes that are less likely to crack or sunburn compared to trellissed or staked tomatos