Do you mean to protect them from being claimed by someone else?
A copyright is generally something that exists once you publish a track. To protect unpublished tracks there is an old fashioned method of posting it to yourself via registered post in a sealed envelope, which can then be opened in court to prove you wrote it first.
I know that PRS used to have a form you could send in with some notation, but they don't do that now it's digitised.
I think the UK musicians Union may have a service for members, not sure if they still do that.
However copyright isn't always that simple. See here: