A method for determining the location of a rover unit with respect to a boundary in an animal containment system, comprising: defining the boundary using a wire , the boundary defining an area within the boundary and an area beyond the boundary; providing a rover unit adapted to be carried by the animal, the rover unit adapted to deliver a stimulus to the animal; generating a digital activation signal having a plurality of data bits; modulating the activation signal such that the modulation indicates the polarity of the activation signal; transmitting the activation signal by way of the wire such that the activation signal generates a magnetic field about the wire, the activation signal having a polarity within the boundary that is substantially opposite its polarity beyond the boundary; storing at the rover unit information indicative of the polarity of the activation signal within the boundary and the polarity of the activation signal beyond the boundary; receiving the activation signal at the location of the rover unit; analyzing the modulation of the activation signal with respect to the information indicative of the polarity of the activation signal within the boundary and the polarity of the activation signal beyond the boundary; determining whether the rover unit is within the boundary or beyond the boundary by considering the polarity of the received activation signal with respect to the information indicative of the polarity of the activation signal stored at the rover unit; not delivering a stimulus to the animal when the rover unit is within the boundary; delivering a stimulus to the animal when the rover unit is within the boundary and subsequently moves beyond the boundary; not delivering a stimulus to the animal when the rover unit is beyond the boundary and subsequently moves within the boundary; and not delivering a stimulus to the animal when the rover unit is beyond the boundary for a predetermined period of time. defining the boundary using a wire , the boundary defining an area within the boundary and an area beyond the boundary; providing a rover unit adapted to be carried by the animal, the rover unit adapted to deliver a stimulus to the animal; generating a digital activation signal having a plurality of data bits; modulating the activation signal such that the modulation indicates the polarity of the activation signal; transmitting the activation signal by way of the wire such that the activation signal generates a magnetic field about the wire, the activation signal having a polarity within the boundary that is substantially opposite its polarity beyond the boundary; storing at the rover unit information indicative of the polarity of the activation signal within the boundary and the polarity of the activation signal beyond the boundary; receiving the activation signal at the location of the rover unit; analyzing the modulation of the activation signal with respect to the information indicative of the polarity of the activation signal within the boundary and the polarity of the activation signal beyond the boundary; determining whether the rover unit is within the boundary or beyond the boundary by considering the polarity of the received activation signal with respect to the information indicative of the polarity of the activation signal stored at the rover unit; not delivering a stimulus to the animal when the rover unit is within the boundary; delivering a stimulus to the animal when the rover unit is within the boundary and subsequently moves beyond the boundary; not delivering a stimulus to the animal when the rover unit is beyond the boundary and subsequently moves within the boundary; and not delivering a stimulus to the animal when the rover unit is beyond the boundary for a predetermined period of time. <EOS>