Between a rock and a hard place

[Railak]

So, one of my players has been doing something interesting, I'm not really against him doing it, just trying to figure out how to make it not a win all kind of thing. So he is a grappling build, and he has a pretty decent burrow speed. He likes to grapple a foe and pull them under ground, then just leave them there like 10 or so feet down.
I don't want to take that away from him, but it'd be nice to find a way that it's not basically fatal to just whoever he does it to every time. He doesn't always do it either, but I never know when he's going to. I'm worried he'll just bury an important enemy. I don't want to just make them ungrapplable either, since he can't do a whole lot outside of a grapple. I thought about giving them a chance to grab onto him as he tries to leave them there, but his CMD is too high.
Aside from the pretty much always fatal part I really don't mind it, it's actually been pretty funny at times too. Like a group of bandits will just be sitting around a fire and then one of them just gets pulled underground. Leaving the rest of them bewildered.

So anyone got any advice aside from make it so they can be grappled, completely taking the ability away, or something he can't just be like "okay, I'll just bury them deeper"

He's a brawler with the strangler archetype, which removes his unarmed strike damage for a very very slow sneak attack progression, he has improved grapple and greater grapple, so he can do 2 grapple actions in a round, he's also able to tap into rapid grappler with the martial flexibility thing of the brawler which would grant another grapple action at a -5 to the grapple check.

[Troacctid]

I remember this coming up in another thread a while back. It's pretty tough to dig yourself out of a hole if you're buried (according to the cave-in rules), and most burrow speeds explicitly don't leave behind a usable tunnel.

My first recommendation would be to simply be aware of the terrain. If you have a fight that you don't want burying to be viable for, just make sure that the floor is made of stone, metal, or another non-burrowable material. Secondly, casters have low CMD, but they should also have the means to escape from underground via teleportation, or no-sell the grapple via freedom of movement. In particular, the latter would be a natural pre-buff for enemies who are expecting the party. Third, remember the action cost. It takes a standard action to move the grapple half your speed. Usually that means it will take two turns to set up, and the other enemies can try and beat on him in between the initial hold and the movement. And finally, Pathfinder introduced a nifty addition to the grapple rules: if you try to move someone into a hazardous area, they get an extra free attempt to escape the grapple, with a +4 bonus on their check. This certainly qualifies.

[H_H_F_F]

I wouldn't try to shut the player down too much intentionally. It's what he does, it takes two turns to execute, and it only works against (relatively) small foes with no means of teleportation. If an enemy is familiar with the party and their capabilities, they'll prepare accordingly. If they aren't, and they're the vulnerable type - well, make sure the plot doesn't depend on them, and let the player enjoy his win.

[Railak]

I remember this coming up in another thread a while back. It's pretty tough to dig yourself out of a hole if you're buried (according to the cave-in rules), and most burrow speeds explicitly don't leave behind a usable tunnel.

My first recommendation would be to simply be aware of the terrain. If you have a fight that you don't want burying to be viable for, just make sure that the floor is made of stone, metal, or another non-burrowable material. Secondly, casters have low CMD, but they should also have the means to escape from underground via teleportation, or no-sell the grapple via freedom of movement. In particular, the latter would be a natural pre-buff for enemies who are expecting the party. Third, remember the action cost. It takes a standard action to move the grapple half your speed. Usually that means it will take two turns to set up, and the other enemies can try and beat on him in between the initial hold and the movement. And finally, Pathfinder introduced a nifty addition to the grapple rules: if you try to move someone into a hazardous area, they get an extra free attempt to escape the grapple, with a +4 bonus on their check. This certainly qualifies.

Yeah terrain definitely makes a difference for that ability. And teleport abilities are definitely viable. These are the kinds of things why I post on here, people the d to think of stuff I don't. Freedom of movement on the other hand, kinda just negates his ability to grapple all together, though rarely are they only going against a caster or group of casters, there's usually a beefy guy he could grapple with.
The last part the +5, I've known about, doesn't really help enough to make a difference.
I understand the normal action economy of grappling, but his action economy is different with it. He has greater grapple, which allows him to do 2 grapple maneuvers in a round, one as a standard action, one as a move. He can also activate his martial flexibility to give him rapid grapple for a minute which allows him to make a 3rd grapple maneuver at a -5, as a swift action. (I sorta said this already, apparently not clearly enough)
So he can initiate and grab hold with his standard, then using his move action, move them half his speed, which puts them 10+ft underground. And that's not even with rapid grapple.