Brass finish security screws

Secure? Fasten it through big lumps at the back. This may involve brazing to the back of your lion to attach loops, then mortaring in some hoops of bent rebar.

Moderate security through its screws - go for the biggest you can, buy bronze ones from a boat chandler (at hilarious prices) with hex or pozi heads and then munge up the heads after installation with a drill. To remove eventually, drill their heads out carefully.

Be warned, tea leaves have better cordless drills (and grinders) these days than you probably do. If they're stealing for scrap, they're also happy to leave the bolted corners in situ and just steal the middle

Or as our local pub has, a small sign that reads "It's only zinc potmetal you pricks" beneath their "bronze" fountain.