Here are some ideas:
1. temporary, but might help or alleviate the problem. If you have an outside water spigot attach a reliable leak-free standard garden hose with a shut-off nozzle to the spigot. Turn the spigot on half way or more. Run your automated sprinkler system. When the valves turn off, the pressure shock that causes the hammer will be absorbed by the hose. It is more effective if the spigot is close to the valves. This may be a temporary solution depending on the degree of the problem. Some people leave pressure on their garden hoses all the time, but I think it is better if you don't.

2. A more permanent fix is to install a pressure regulator before your arrestor. Higher water pressure will accentuate water hammer. After installing a pressure regulator, you may still need to add more surge arrestors. If you can't install a pressure regulator, or if you need the pressure, you'll just have to add more surge arrestors or larger arrestors (make your own using a 4 ft capped copper pipe).

hope this helps,

Hi Tennfescue,

Google Water Hammer Arrestor. You should affordably be able to find what you need. Do you know how to solder? GL Aloha.

I had the same issue. This fixed it. http://www.cashacme.com/prod_sharkbite.php

If your system is programable one thing that will help is to have an overlap in the switch from one zone to another. That way there will not be a complete stop in the flow during zone switching. This however will not stop water hammer if it occurs when the system first starts up. However it does not cost anything other than time to reprogram the switch overs. A more permenant fix would be to install a small precharged pneumatic tank (well pump bladder tank) between the line in the garage and the line out to the zones. It will absorb the shock very well if sized correctly.