51% guarantees you retain ownership.
If your corp is in good shape, you'll see your stock split several times soon after IPO. Hang out at 85% or something high while this happens...splits usually happen around 100$/share.
Pretty soon you'll have over 1 billion shares, you corp will be worth a lot more, and eventually the stock price will start to level out, or at least stop growing so fast.
At this point you have choices. Hold firm, sell shares for cash if you need it, or aim for "truly public" wit 24.99% ownership
51% guarantees ownership...but if you are willing to give up guaranteed ownership, go down to 24.99, the corp becomes "truly public" and will upgrade itself beyond the normal maximum...this has several very beneficial effects: Higher salaries, more profit, more taxes\profit sharing\dividends. I haven't gotten to this point yet, but I have a pair of corps on the way there, and I'll be finding out soon if its worth it.
As long as no other shareholders exceed you 24.99%, you still run the company. If someone really really wants to take ownership, they will have to buy probably a billion shares to exceed your ownership...as they do so the stock proce is going to go up and its not going to be cheap for them. But remember two can play at that game...you just have to buy enough shares to get above him, or back up to 51%.
Frankly I don't see this happening often. Maybe don't do this with your weapons firms or other critical corporations, but for most companies I don't think you run too much risk of losing control. Maybe someone can correct me on that...