While not in Ontario, my goal is always long term, full time families. At interview, I ask the questions about if they are planning to move to a center at 18 months, and if that is their goal, then I don't offer them the space. I also turn away teacher's expecting to pull their child at the end of June and full time students whose course typically ends in May.
Further, I no longer charge a deposit on my spaces but instead charge a two week enrollment fee. If and only if someone has been in my care a full year min when they hand in notice, then they are given a credit to their final weeks that equals the enrollment fee. If they depart the day care before a year, then no credit is given. Because two week's fees is quite a substantial amount, it does help to weed out those who know they are planning to leave in a few months time. Since my notice period is 4 weeks and fees are due regardless of attendance, then with the enrollment fee I have 6 weeks of fees to financially assist while seeking a replacement.