To be honest, the harder you make it to copy, the more likely people are to copy and re-publish it, purely out of spite. There are many legitimate reasons for people wanting to highlight and copy text that don't involve plagiarism, and if you try to interfere with that in any way then you will become very unpopular, and your site will become very unpopular. And the people who have copied your content and made it accessible on their websites will get all of your traffic.
If people want to copy it, they will find a way to copy it. If you're going to publish it, you can't stop them, and it isn't worth trying - and that is particularly true if you want it spiderable. Any method you use will make it more difficult for people to read and interact with the site in they way that they want to.
Sure, some people may copy what you've written? Is that the end of the world?