A metal barrier or a doggie seat belt or a kennel or something different that I'm unfamiliar with. (Tell me more if it is!)
If it's a barrier, we've always just bungee corded old ones into new vehicles (on the headrests and the bottom of the seats instead of buying a new one everytime. Yeah, there might be gaps, but none big enough for the dogs to get around. For kennels. . .I've always found something to bungee them to as well.
Of course, the seatbelt kind are pretty self-explanatory, so you wouldn't be asking about that, I guess.