As others said, the growth battle is where you will usually see the biggest issue. IME, most montis will have little turf wars where they touch, but it doesn't result in any major damage. In the end one keeps pushing forward more than the other and starts to gain ground. I have my setosa, along with a pokerstar digi and forestfire digi all growing on the same rock. They've basically covered all available real-estate and at this point I keep them in their little corners by occasionally taking the rock out and killing an inch or so border area between each monti with superglue and only allowing them to grow outwards/upwards. Sometimes if I'm more industrious I'll take my chisel gouge to them and hack out the middle areas to make some frags, but that's a lot more work that breaking off outer areas.
