Specifically: what are some biological structures that could help subvert the square-cube law's effects on animal overheating?
Bob is a really, really big land-based ambush predator that's normally sedentary but that puts on massive bursts of speed in order to catch his prey.
The problem with this is, like with many such things, the square-cube law. Specifically, big animals have issues dumping heat quickly, since they have more volume, and therefore, mass, relative to their surface area. Therefore, if Bob exerts himself for too long, Bob will overheat, and it won't be pretty.
When at rest, or going for a stroll, Bob doesn't produce enough heat to overheat himself. He might be warm to the touch, but he's doing fine in terms of body temperature. However, when Bob is running, fighting, or otherwise exerting himself, he can't dump heat quickly enough to stay alive. Sometimes, Bob has to do these things for a long, long time, because his prey has a tendency to run him down over the course of day-long periods if they believe he's responsible for any deaths in the area; as such, limiting activity to brief bursts is not an option. As such, please do not answer with this.
A common solution I've seen to this would be to make Bob less dense. However, Bob's prey is very good at fighting back with a wide variety of lethal weapons, and so Bob needs to be as dense as water, on average, in order to contain enough mass and therefore enough bodily structures to fight well and withstand damage long enough to heal. As such, please do not answer with a decrease in Bob's density, because Bob would rather not die, thank you very much.
Please note that I am referring to biological structures, not behavioral adaptations - "biological structures" in this sense include the brain, the blood cell, bones, and other such things, whereas "behavioral adaptations" are things such as "this animal is aggressive" or "this animal is nocturnal".
Additionally, please note that I am not interested in determining what evolutionary pressures might lead to this. Assume it's being built in a mad scientist's lab.
Good answers will will cite a biological structure/bodily feature/design adaptation/etc. capable of storing, rapidly dispersing, or otherwise mitigating heat that's also capable of existing under Earth-like conditions and that is compatible with Earthly biochemistry.