Hi My Housbant His Take Methadone Form July. His Now

Hi my housbant his take methadone form July. His now on 10 ML weekly. Buy l woried then hi start take heroin again sometimes. My questions is how l can recognised is his on heroin or not? ? His going every Friday to his doctor and test is ok, but if his takings heroin on fraiday after his appointment so in the next Friday the test is not show the heroin.because heroin in your urine is only 2-3 days?????please help me.thank you