Busted rad x2 after rebuild

Hi there, I hope someone can help me. I have a 1996 Range Rover which had an engine rebuild in the latter part of last year, that in itself was expensive enough £3k by the time I had a lot of incidentals on top. The problem I have now is this, after the big job was done I did only 1500 miles and the logo flew off the fan and straight through the radiator, ok so we got a new one, then another 1000 miles on something was sucked up from the road and again another radiator, then last week after another 1800 miles it happens again. Now I am scared to go out in case it costs me another radiator, I have ordered a cover for the underneath so as to protect the rad, (it seems the original one has been long gone) Is there anyone out there that has heard of this problem, what is the cause, could it actually be something the repair garage has done, or not done, as the case may be?? The garage owner has been most helpful, not charged me yet, as he said he wants to see me do at least 3000 miles before I pay for this latest rad. My son thinks it could be something to do with engine movement, who knows, please HELP