What is the test for overt acts of concealment in criminal proceedings?

I reject the argument that overt acts are required and in so doing adopt the language of Lord James in Bulli Coal Mining Company v. Osborne [1899] A.C. 351 at page 363, as follows: "The contention on behalf of the Appellants that the statute is a bar unless the wrongdoer is proved to have taken active measures in order to prevent detection is opposed to common sense as well as to the principles of equity. Two men, acting independently, steal a neighbour's coal. One is so clumsy in his operations, or so incautious, that he had to do something more in order to conceal his fraud. The other chooses his opportunity so wisely, and acts so warily, that he can safely calculate on not being found out for many a long day. Why is the one to go scotfree at the end of a limited period rather than the other? It would be something of a mockery for courts of equity to denounce fraud as "a secret thing," and to profess to punish it sooner or later, and then to hold out a reward for the cunning that makes detection difficult or remote."