Un intentionally prevention of Ehtelam is involuntary and hence out of control by a man. However; one important thing to note is that intentional prevention of Ehtelam is also not possible. Prevention of urine to pass is some thing else. During Climax either in Ehtelam or in sexual intercourse, a man reaches to the stage of no return. At this stage, the pressure of semen increases to much and the external sphincter of urine tube that hold urine or semen is dilated. One can't prevent ejaculation or ehtelam if he enters into such stage. By external measures like making the tight grip around the outer end of penis with thumb and fingers, the external sphincter could be constricted and ejaculation or ehtelam is prevented. This external pressure is the same method which is used in Squeeze technique for the patients of premature ejaculation. However; the squeezing is done just before climax since if a man crosses the border of climax, his ejaculation or ehtelam could even not be prevented by this measure as well.

What could happen if the Ehtelam or ejaculation is prevented before climax? the desire to ejaculate or Ehtelam would be prevented or vanished automatically or if the semen is entered in the urine tube or near to it, it would go back either into seminal vesicle or in bladder that would come out with urine after some times. The forces and pressures die out and the condition normalizes. 

Another way to prevent Ehtelam or ejaculation is by the obliteration of outer hole on the glans penis. In this way however; the pressure of Ehtelam or ejaculation could be lethal to the walls of outer urine tube, but in reality this is rear to do.

Other Relevant Threads To Read: