A shotgun clause is probably the best method out of a bad lot, but it still has the potential for abuse.

If a partner is going through financial difficulty (outside of the company), then the partner with a better financial position can force a sale at a depressed valuation.

Say my mother has a massive stroke and requires expensive ongoing medical care. After a while, I'm financially drained. At that point, my partner can trigger the shotgun clause at an amount larger than my ability to scrape up cash, and wham I'm out. Out with a small payout, but out regardless.

There isn't a silver bullet to these kinds of issues. At the end of the day, people are involved, and people are complicated and difficult.