Honestly, I don't think that sabotage is all that difficult, not to say that it is common.
In the case of whereabouts violations, they are unsatisfying because the requirements are difficult to meet. Forget three times in 365 days? Hardly unlikely. You get it right 362 days and get it wrong 3? That's a tiny margin for error. Within those 365 days, you have to be exactly where you said you'd be for an hour. What if you got called out to your parents' house for a medical emergency in the middle of the night and missed your early morning window? What if you gave one address and then moved and forgot to change it? What if your agent said get on the next flight, you are racing in Europe tomorrow? The system includes within it far more possibilities for error without intentional cheating than the drug tests themselves. So, there will always be that ambiguity as to whether the player skipped the tester to conceal doping or just forgot or made a mistake. That's why in all these cases, the tester needs to immediately follow up with the athlete until the test sample is collected, so that it's not just a matter of being at the mall at the end of the testing window.