Lord knows (that) I've tried

Lord knows

1. No one knows (except for God). Lord knows how long it will take for my application to be processed. A: "How do you think you did on your exam?" B: "Lord knows!"
2. It is absolutely true, certain, or definite that; it is obvious or clear that. Lord knows I need to do well on this test or I can kiss my scholarship goodbye!
See also: know, lord

Lord knows (that) I've tried

It is the absolute truth that I have tried my best (to do something). A: "You and Jeff just need to spend some time together and bond." B: "Lord knows I've tried. That boy just isn't interested in doing anything other than playing those damned video games." A: "You need to convince her to accept the deal." B: "Lord knows that I've tried, but she is adamantly refusing." A: "Then try harder!"
See also: know, lord, tried

Lord knows I've tried.

Fig. I certainly have tried very hard. Alice: Why don't you get Bill to fix this fence? Mary: Lord knows I've tried. I must have asked him a dozen times—this year alone. Sue: I can't seem to get to class on time. Rachel: That's just awful. Sue: Lord knows I've tried. I just can't do it.
See also: know, lord, tried