Is it possible to make a Tenai [condition] that any money I think to donate to Tzedakah is an invalid donation until I actually give it? I would want to do this because a Meshulach [collector] may come over to me, and I may decide to give him a dollar or something, and then he may turn around and leave. I know that the obligation to give Tzedakah can be established by thought and doesn't need a physically donation to come into effect, so I am worried that I'd have to chase him to give it to him.
My questions:
- Does my concern even require resolution?
- Would the Tenai outlined above actually help?
- If it wouldn't, what else can one do?