Have you ever noticed that your Greyhounds' head is narrower than his neck? Most other kinds of dogs' heads are wider than their neck and that keeps their collar secure when out walking. However, it is very easy for a Greyhounds' collar to slip over the head with potentially fatal results. I discovered this first hand one day when I was out delivering door to door. One of our Greys, Katie, likes to come with me when I am doing this and as we were walking along I thought that the lead felt a bit light. I looked behind and discovered that I was dragging an empty collar and lead along the ground with Katie trotting along a few yards behind. The collar had slipped right over her head. I was lucky this time, there weren't any cats about, if there had been I may never have seen Katie again, as with all Greys, she would have been off so fast that by the time she realised she was alone she would have been lost. (That's Katie at the bottom of this essay.)
What is the answer to this? Well it is certainly NOT to overtighten the collar. Obviously it should be resonably secure but if it is too tight your dog may choke or be unable to breathe. Certainly he will be very uncomfortable. The first thing is to always be sure that you are behind your Greyhound. Don't get in front or he will be able to simply back out of the collar and leave you holding an empty lead like I was. Better still, use a Halti, (see "Pulling on the lead" tip on this section.) Even if your dog doesn't pull on the lead a Halti is also the answer here as well. Most dogs soon become accustomed to them and accept them happily, however, if yours doesn't and is not a problem with pulling, then you could try a body harness instead. Whilst these are useless to correct pulling, indeed, they make it worse because the dog has his whole body to pull with, not just his neck, nevertheless, they are better than just a neck collar for security. If you don't want to use either of these methods then please stay at the rear of your precious Greyhound. If he backs out of the collar you may never see him alive again.
Since I wrote the above I have learned of a non-slip collar for Greyhounds. It looks a little like the choker collars which we certainly would never advise you to use, but these are different. They can't over-tighten as can choker collars, but if your dog starts to pull back the collar tightens just enough to stop his head slipping through. The material that they are made from is a non-slip type that seems very secure to me. The best way for you to see what these collars are like is for you to see one yourself so below is a picture of one. There is also a very good range of collars for Greyhounds at www.kitschcollars.co.uk