Simply making the hash really hard is not a good option. All most people will notice is that their underpowered phone suddenly takes way longer to unlock compared to before. Cracking the hash on very powerful hardware is then 'trivial'
As the other comment mentioned, a hardware solution seems to be the only one.
Seeing as you had about a 3 frame window to line up the middle one (and pure chance to line up the bottom one), don't be too hard on yourself