We've been trying to line a bitch recently but they don't seem to be tieing, she is 15 days today we've had to restrain the bitch evertime we are trying as every time the dog goes near her she's at him, he's been in a load of times for a good length of time but keeps slipping out without tieing, has anyone else had this problem? Or has anyone got any suggestions about what' going on? Atb