Can I withhold visitation rights to drug using ex-husband?

I have an interm order in place allowing my ex-husband to see our youngest child only. He is an active drug user, but had passed a court ordered drug test. Both my lawyer and I are aware that he is still using drugs, but know by the time we get infront of a judge and he has to get the urine test, he will pass it (3 days lemon juice and water, his brother is a lab tech and he has used that to his advantage over the years). My youngest is with him and his safety at most times is questionable to say the least. I do not feel safe, want to revoke these rights but i feel i have no choice but to allow him into harms way and hope to god each time he is safely returned. Do i have the option to withhold untill another form of testing or investigation is conducted? -- Aly