I know some people cover the area with spiky twigs till the seadlings come though, once the seadlings are big enough you can remove them and the cats shouldn't bother them.
In our case it's the neighbours cats who are the issue so I'm happy to use wide ranging things and keeping them out of the garden entierly. We've had some sucess with the ultra sonic deterant boxes, it kept the cats away and provided it was set in an area we didn't need to go too often the batteries lasted OK..However the post to stake it in the ground was nto that strong and has broken off so I need to find a new way to fix it up.
There are some granuals/gel which we've used in the past to keep cats of certain areas. They end up quite expensive though as you have to replace them quite frequently.