Given it only costs 10 Discipline, lasts 30+ seconds and (AFAIK) can't be killed by monsters, unlimited turrets would be pretty imba in a boss fight. But it doesn't actually specify the limit on the description, whereas most pet skills do. Hopefully this is just an oversight in the text.
Compare with Hydra, which is a very similar skill with similar damage output, but with a definite limit of 1 Hydra at a time.
I was asking exactly because desription doesn't give an answer. Also turrets duration can be doubled with Custom Engineering. But that way it would lead to turret forests being planted which ould be cheesy but thats the only way one could really play "healing hunter" or "invicible hunter".
With just base skills of preparation and sentry one could have 6 turrets already, thats not including any runes or +discipline gear. But how else can we play trapsassin in D3? :(
I was wondering the same question, but i could almost bet that you can't have multiple up or at least the amount is limited. Proper passives, preparation and some planning you could get 30 turrets up simultaneously no problem.