If you really never want it to move, you could resin fix in some bolts to the brick, we did this, and there is no chance it is ever moving...
Super-Long-Term- I'd put money on us re-instating the fireplace.
Resin fixings probably overkill then! We have a couple of TVs only up on gripit fixings, and they haven't movced in 2 years, so a combo of brick screws and those should be fine.
@deleted started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
If you really never want it to move, you could resin fix in some bolts to the brick, we did this, and there is no chance it is ever moving...