When you get a new will created, it should be standard that the first part of it is declaring you of sound mind and that this will supersedes all other wills and makes them null and void.
Both my parents have now gone, my mum being the last one to pass away and she had no will so was an intestate person. But interestingly the solicitors that we (sister and I) instructed were only going to call other solicitors to check they had no known wills within a 3 mile radius. Which means, in theory if your family know about a will, they could get round it by going to a further afield solicitor and claim there is no will.
I believe there is a national will register, but I do not know if that is a mandatory requirement to register you will on there.
Other way is to get a solicitor to create you a will, then appoint a non beneficiary executor (someone that will know you have passed away) that will make the beneficiaries know about the will and enforce the will through to conclusion. But, as already stated above, still will not combat those who may not respect your wishes and contest the will in court.