Whither the Canaanites?

One thing some students of the Bible find puzzling are apparently conflicting statements about the actual scope of the destruction of the Canaanites. On the one hand we have unqualified statements about the decimation of the Canaanites (e.g. Deut 7:2; 20:16-17; Josh 10:40-42). On the other hand, we have statements acknowledging the continued presence of Canaanites in the Holy Land (e.g. Judges 1-3).

This also crops up in debates over the historicity of the accounts. Does the archeological record confirm or disconfirm the extent of the conquest in biblical narratives? 

i) Many scholars say the Biblical language is hyperbolic. Hyperbole was a stock literary convention of ANE conquest accounts. And I think that explanation may well be valid. 

There are, however, one or two alternative explanations:

ii) To begin with, we need to distinguish between commands and compliance. You could well have discrepancy between the scope of the command and the degree to which that was carried out. That doesn't mean the record is inaccurate. Rather, that means the Israelites were not consistently faithful in implementing the command. 

iii) Finally, Scripture indicates more than one way in which the Holy Land was cleared of Canaanites. Mass execution was one means. But Scripture also refers to expelling the inhabitants (e.g. Exod 23:28-30; Lev 18:24; Num 33:51-56; Deut 7:20; Josh 24:12).

Now, to the extent that many Canaanites were driven out, that means they were still alive. So even if they self-evacuated, they–or their descendants–could stage periodic raids or military incursions. Attempt to reestablish their presence. Retake land which they previously occupied. 

Ancient Israel had porous borders. It's not as if there was an electrified fence to secure the boundaries of the Holy Land and keep intruders at bay. An area which might have been free of Canaanites in the time of Joshua might be reoccupied by Canaanites in the time of Judges–absent constant vigilance by the Israelites.