Hey there, please forgive the lateness of my reply.
First of all, addressing the issue regarding penning monsters; you're 100% correct, their behaviour is not yet ideal. Monster wandering has always been an interesting challenge, if you played the game during it's earliest iterations, you'll remember that this used to happen around the edge of your garden as well. Essentially what's happening here is the navigation mesh (UE4's pathing system) does not get updated properly, and monsters do not register interior fences as obstacles.
It was hard enough figuring out a system for keeping Resident monsters from trying to explore outside your garden, while still allowing Visiting monsters to roam where ever they please. However, I definitely plan to fix this before the final release of the game. Monster behaviour and wander mechanics will be confined to defined pens.
Lastly, regarding monsters engaging the player; this has always been a planned feature for the game, and will be tied to the Loyalty system, "if you neglect monsters they may take out their frustrations on you!" The loyalty system is very loosely hashed out at the momeny, providing a basis for monster happiness, but not yet providing a penalty for neglecting them. In the final version of the game, you can expect the events you described to occur, as well as monsters ignoring you should you choose to instruct them in the Arena.