Your code itself is automatically protected by copyright regardless of the licence (unless you explicitly place it in the public domain).

As for the ideas behind it, yes a patent would be the only way to restrict others from using them.

A software patent application may not be something you really want to go through though: it's not possible to get in many places, time consuming & expensive, and it may turn out that the required patent search (which in itself can be quite expensive as well) will turn up that your brand new idea actually has "prior art" implementations. Not to mention that many people believe software patents are evil ;-)

Note also that the GPLv3 has some additional requirements regarding patents, you should read them and understand them before deciding if it's suitable for your needs.