I had 100% success this season on apples, pears, and plums by
- Wrapping the scion in parafilm before I grafted.
- Wrapping the graft union site in parafilm after grafting.
- Using Temflex tape as discussed in Budding tape.
- Using this grafting tool as discussed in Zenport/Generic grafting tool
My prior success rate using different knives for cleft and splice grafts was about 50%.