I find it easier to get a sighthound to comply to a "release" word, rather than a recall command. (That said, my three DH's have excellent recall, but I doubt I would have 100% recall if they were on to something). Best not to start something you cannot stop.
If my dogs spot something they may like to chase (be it a cat, native animal etc), then they will wait for me to say the "release" word. Of course I do not say it in these instances. Instead there is a short sharp "UH!", and they will just watch.
If they spot something they are allowed to chase, or that I wish them to chase (such as the lure, or the fox that was stalking the lambs one evening a few weeks ago), they are given the "release" word (I use the word "rabbit"), and will give chase.
This means I can also use the "release" word to get them mentally "revved up" before coursing, or if showing in a lacklustre manner, by asking "where's the rabbit"?