I've squeezed bikes into pretty small spaces indoors. In one apartment one lived in the shower. Was it a pain to move it all the time? Yes. The bike didn't get stolen though. Eventually we decided we had other space for it. Usually you can find a little floor space if you really want to bring it in. How important is having the bike to you. If it is important to you, you find a save spot outside or more likely will make space for it inside.
Folding bikes can take up very little space if that is an option.
The ground anchor mentioned in an earlier post might be an option. If googling for options I think they are also called hurricane anchors. How well they hold may depend on the soil, but the ones I put in to anchor my shed are crazy solid they'd be really hard for a theif to get out with a bike locked to them. An angle grinder would cut them off easily, but it would also cut pretty much any lock so It really wouldn't necessarily be an especially weak link. Some may have a weaker or stronger loop or eye on the top. Keep that in mind when choosing. Also place where it isn't a tripping hazard.