Mobile Ad-hoc Networks (MANETs) are based on a fundamental aspect, which is the cooperative parameter. This parameter may compromise the networks. The selfish misbehaving nodes can seriously affect the network performance. Moreover, the existing mechanisms based on the monitoring process to detect the misbehaving nodes are not efficient and suffer from an important false alarm rate. These weaknesses are mainly due to the interferences and the costs of the monitoring process. In MANET based on $SISO$ (Single-Input Single-Output) technology, the interferences at the monitor node compromise the observation and the accuracy of the cooperation report. That is why in this paper, we focus on the MIMO (Multi-Input and Multi-Output) technology to overcome these drawbacks and to significantly improve the monitoring process. We propose a new MAC protocol called MIMODog-SPACE-MAC based on the well-known SPACE-MAC protocol. It allows the monitor node to avoid the collision during the monitoring process by adjusting the antennas weights in order to nullify the signal coming from other nodes than the monitored one. Therefore, the proposed solution contributes to significantly enhance the accuracy of the monitoring process. We show that for a MIMO network with randomly located nodes $n$, each equipped with $M$ antennas, the achievable number of monitor nodes is $\Theta(\frac{M}{\sqrt{n\ln n}})$. Indeed, theoretical results show that by using MIMODog-SPACE-MAC, the network can have a constant improvement $M$ on an asymptotic number of monitor nodes compared to SISO 802.11 DCF MAC.