Much as I'd love to see Putin assassinated, and / or the Russian military forcibly driven out of Ukraine I think this article suggests that what the west is currently doing is probably the best approach.
https://www.defenseone.com/ideas/2022/03/how-stop-putin-without-starting-wwiii/363062/
TL/DR - send lots of small arms, anti-tank, and anti-aircraft arms to Ukraine and support the refugees when they arrive in a NATO country, but do not get drawn into a war.
I see comments on this thread that Putin will not stop at Ukraine, and while I concede that Putin's desires probably extend beyond Ukraine, I suspect that since Ukraine is proving so costly that it has served as a significant reality check for Putin.