It didn’t matter how careful they were, somehow Splinter always seemed to know what they were up to.
Mikey often joked about their father having a sixth sense for trouble; Leo argued that it was because he was spiritually connected to them, but even he had doubts. Donnie thought their father just knew them well enough to guess what they were planning. Raph just found it annoying that Sensei could stop them having fun.
Splinter patiently waits for the day that one of his students slips under his radar; because that day he’ll know that their training is finally complete.