I'm thinking that Mary and Richard probably got married in Ditchling, and that's why you can't find that record as well. If they don't have them in Chichester, they might be in the East Sussex Archives in Lewes. My own Eliza Oram, who was one of my great x something grandparents, was also born in Ditchling, but luckily her parents weren't and they were on the census so I could trace further. I think it would be a good idea to try and get the Ditchling records, even if you have to pay for someone to look for you, if you can't go yourself. I was thinking that myself, or he could have been visiting someone else on the census, or he could have just run away! let me know what the death certificate brings up, and good luck with the record offices!