
Tieing is what generally happens with canine copulation.
The male has a bulbous gland at the top of his member that swells within the bitch and this causes him to remain tied within the bitch for anything from a few minutes to half an hour or so. t
Te dog will usually also turn (lifting his hindleg over the bitches back so stand back to back).
This is not needed in order for the bitch to become pregnant as ejaculation of the semen usually occurs within the first minute of entering the bitch.
As for timing bitches vary as to when in their season they ovulate, some as early as the first few days ans some very late or even when most bitches would ahve finished, so it is alwqays wise to keep bitches seperated from males for longer than 21 days.
Also a bitch should be watched even in your own garden as you have found out. If the male dug his way in chances are he caught her at the optimum time.