How do people pay fines? If they are unable to pay what are the penalties? You also just created a black market for people who still want to smoke and that'll produce all kinds of fun.
Black markets are a reality under current economic conditions, and they're a reality even in completely legal markets (there's always someone willing to pay XX% less in exchange for YY% more legal risk). Putting extreme taxes and/or fines on smoking might pour gas on that market, but long-term trends just don't support its survival.
And as for fines: we already have a legal structure for that[1].
But there's also a trend against long term damage here: smoking rates have been declining for decades, and the evidence overwhelmingly suggests that higher taxes and civil penalties (like fines for smoking in parks) do reduce smoking across all ages and demographics. Fewer people smoking overall means fewer people who are subject to any sort of systemic abuse. That feels like a decent tradeoff to me, especially when we consider the knock-on effects of smoking itself (individual and community health, pollution, dental outcomes, &c).