I've not used that Roland device, but have found different triggering units differ greatly
in what parameters they offer for preventing false triggering. This is particularly
important if triggering from acoustic drums, as opposed to pads. You might check out some
different trigger units.
Another option would be to use pads instead - they
won't suffer this problem.
Other than that, as has been suggested, monitor
quieter and/or use headphones / IEMs.