Zoomies can be a big problem for some dogs and greyhounds are no exception. A zoomie is when the dog takes off running laps around the ring and ignores the handler. Most often, I believe it is caused by stress. Some dogs respond to stress by shutting down and others simply explode and lose all control.
I had some trouble with Riley in early training. She would periodically start spinning and zooming if we were working on something challenging. I worked very hard on teaching her to recall out of a zoomie just in case it ever happens in the ring... Knock on wood, it has not.
I have a couple of strategies for dealing with zoomies. One, you have to have some way to take the edge off at an event. The dog needs to be able to burn off some steam if that is what is needed. This is why I love teaching all of mine to fetch a toy. It is such a great way to allow for some controlled free running and on a long line if you need the added security and there is no fenced area. Click Here for teaching a play retrieve.
Also, I think it is important that the zoomie-prone dog has ample opportunities to zoom. If the dog really runs his tail off on a regular basis, he will be less likely to explode when you need him to listen. He will be in a better frame of mind for dealing with stress.
Riley is allowed to zoom after each training session. Some folks would suggest that it is not a good idea to allow Riley to do this inside of an agility ring as she may not know the difference between when she is allowed and when she is not allowed. I disagree. Permission is granted with the verbal cue "playtime" and she is given a Zanie Flyer.
This strategy worked very well for all of Travis' life as well. His bumper granted him permission to run all of the laps he wanted to. Here is an old video of Travis zooming from February 2008 (my very first Youtube video :-). He was 9 years old.
Make sure your dogs have super reliable recalls if you allow zooming outside of a fenced area or in an enormous fenced area such as in Travis' case. At any point, I could have called him over to me. He had to prove he was extremely reliable before being given that much room to run.