yup, 'solid core' (i.e. mono-filament) is the key. multi's are very vulnerable in the crosses.
I use gut in the mains and ashaway liberty 16 nylon in the crosses... a very nice combination. the gut provides the durability and the playability, while the liberty nylon has a rough and tacky surface that 'grabs' the mains well so they don't move around that much.
although after 3-4 weeks (yes that's how long the job lasts for me, I hit a flat ball), the nylon does get worn down a little and gets more slippery so the mains tend to move more, but that's about when the main breaks anyway.