It doesn't have to be 50+1. If fans just had 25+1, it would be enough to stop a special resolution being passed. Or some sort of 'Golden Share' that ensured a say or veto over key decisions.
But it needs more than that. These issues have arisen because football became a financial arms race. The only way to win it was to spend more and more. Look how much money we needed to spend to get a regular top 4 spot. United haven't even managed a regular top 4 spot with all their spending.
An effective version of FFP, not the abortion we have now, is needed. As I said, I'd go for the NFL model. The PL already negotiates a central TV deal so why not kit deals and major sponsors as well. Probably get more doing it that way than the 20 clubs doing it individually. It's proven that collective bargaining is more effective.
Then, like the NFL, agree that a certain percentage of the take is going to the players and apply a hard cap, which is the same for each club. Let's say that's 80% of the central revenue, with the PL keeping the other 20%, most of which goes to the grassroots. The TV deal alone is worth £5bn over 3 years and I reckon you could easily treble or even quadruple that over the same period with sponsorships and kit. That's something like £6bn a year, split 80/20 so giving s £240m to each club per annum, with a wage cap of say £180m.
Then add on tickets and any local commercial deals, revenue from use of the stadium etc and that's probably something like £400m total revenue for the bigger clubs, of which only £180m is going in player wages and say, £80m in other expenses. That's £140m profit a year and a much more competitive league.
And then there's CL money but you don't need that just to stand still, as at present. It's the icing on the cake and not a financial disaster if you don't get it. Those top 4 clubs could be turning in profits of £200m or more.