How to plan a surprise proposal?

I’ve been reading about wedding proposals for future purposes. I am really interested in doing a destination proposal, but I want it to be a surprise. What are some ideas for pulling this off? I think a lot of times when planning something big or really romantic, you can send off the radar of your S.O. This is for the future, but I am interested in planning now. If the whole trip is a surprise, I feel like that could set off her radar, but at the same time a surprise vacation out of nowhere would be a shock in a great way!

TL;DR How to plan a surprise getaway/destination proposal without alerting the S.O.?