emmathestar,
Urine testing for a wide variety of drugs is quite easy to mask. All of the methamphetamine masking ingredients are conveniently available at your local 7-11. Blood test masking is extremely difficult, although that is often only used here if the police believe that they have a strong case already (it's quite expensive), with urine tests being the normal vehicle of testing for routine checking.
Regards,
Old Smokey