yeah man i would say that is sluggs, its verrry simmilar to the damage i was getting, to confirm it look your plant over for slugg slime trails (it will just look like snots whipped on a sleeve)... there will also be little balck slugg poop that should contrast against the green of the mj.
was this damage more apparent in the weeks we had of straight rain, with little to no sunshine, because that it prime slugg conditions, thats when i noticed it on my plants. I would rule out and larger animals such as rabbits deer.. etc. becuase they would have taken whole leaves instead of little nibbles around the lefs veines.
as far as slugg prevention there are a couple of methods.. ill go over them reall quick..
to prevent;
- Copper can be used to prevent sluggs, especially when in pots, the mucus of the slugg has a chemical reaction with the copper making the slugg feel as if it is beeing shocked. You can go to homedepo and get copper flashing which you can put in a line aleast an 1 1/2 around the pot, the slugg wont pass this line... the same can be done with copper wire (of course stripped and un-wound into singular copper strands and then wrapped around the pot) I have used this method on my current grow making small rings around the stems, with varying degrees of succsess, from what i have learned the more copper the slugg has to cross the better.
-Diatomaceous earth is also effective in detering sluggs, made from little shelled alge call diatoms, this is commonly used as pool fiters and could be found at any pool store, the slugg hate crossing this as the small shells cut the sluggs up making it uncomfortable for them. However using this can/will lead to a green alge growth if the materials are not replaced after it rains.
To kill:
-old school method..... Hand picking, this is more for a plant that is easly accessable to you aka in your back yard, as opposed to a grow in the middle of the woods that is hard to keep an eye on. the best time to go slugg picking is either at night, or on drizzly overcast days.. this is when they sluggs are out.
- there is a simple beer and saucer method, where it is as simple as it sounds, take beer, and pour it into a pan/saucer the sluggs are attracted by the fermenting of the beer and will crawl into it... only to drowned a drunken death
( you will have to replace the beer EVERY time after it rains, and every 4-5 days as it will fill up with sluggs.) (be careful not to have fingerprints on any of this stuff)
-slugg granuals are sold in the majority of garden stores, especially around us as N.E in general has a slugg/snail problem, you simply sprinkle the pelletts around your grow site and without rain it will last you a good 2-3 weeks... however if it rains, you have to replace it.
- As everyone knows sluggs hate salt, we have all been there pouring it on them at a young age.. well since you are in a pot rather thanin the ground you have an advantage in slugg protection... YOUR NEED TO RASE YOUR POTS OFF THE GROUND be it with 2X4's or whatever, just make sure the pot isn't on the ground (If it is the salt will leech into your pot killing your roots/plant).. you can proceed to put salt around in circles the only thing is you will have to replace this after it rains
If i was you, i would suggest raising the pots off the ground, with 2X4's wrapped in copper, aswell as getting the slugg granuals (but only use them when there is a streach of good weather) Once your pots are off the ground, this will leave a 4 inch area in which you can utilize the saucer and beer method.... this way any slugg going for your plant, will try to go over the copper, say eff that, and be attracted to their drunken death with the saucer right there.