Traps.

"We are going to set up traps for the heroes," you say.

You hear a few skeptical snorts from the goblins, including the shaman. "You think we haven't tried that? They don't work!"

"Not without me, perhaps... Show me."

"I have better things to do," the shaman mutters and calls over a much younger-looking goblin girl. "You. Show our new 'ally' the traps we've laid out around the camp."

The goblin girl nods and walks towards the wall gate, gesturing for you to follow.

While you do so, you take the time to inspect your guide. She's in pretty good shape, with a little bit of a muscle definition and some impressive hips. A lot of her green flesh is also exposed to you due to her rather skimpy fur armour. You'd tap that if you were physically capable of doing so.

First, she leads you to a tree with a bundle of rocks tied up in a rope hanging above the ground. "Here's one. We've set up a tripwire to make sure whoever walks underneath gets crushed, but they never trip on it!"

You can see why. It's pretty obvious where the tripwire is, and even if that one was less visible, there's still a very blatant bunch of rocks right above it. You stroke your nondescript chin with your gloved hand. "I see... What else is there?"

Next you are taken to a pit trap sloppily covered with leaves.

"What about this one?" the goblin asks. "Nobody ever seems to fall for this one either."

She giggles at her own unintentional pun while you consider your response. "I get why. Anything else?"

"We have a few snares laid out around the place. They've worked a few times, but the heroes keep cutting themselves loose..."

"I see..."

You see the same pattern for all of these. They're too obvious, or are just too easy to thwart even if they are triggered successfully. You could either try to get the goblins to camouflage them better and use better rope for the snares, ooor... you could make them more dependent on you by using magic. How obvious they are might actually work in your favour considering the heroes won't expect them to be a threat. The choice is clear, really. You don't want these goblins thinking they can do this by themselves. Then they'll probably kick you out without a shred of gratitude.

"I can fix all of these as long as I'm nearby to cast some spells," you assure the goblin girl. "Can all the traps be seen from your watchtower?"

She shakes her head. "No, why?"

"So you know if someone is approaching, of course."

"Nah, we just check them every day."

"And that's another mistake. Sounds like we'll be doing some deforestation..."