I have to step out on a limb here, and point out that the circular thinking of "if you go to the beach you might have sinful thoughts, so lets call going to the beach a sin," is sinful in itself. It is, in fact, the very thing that Christ fussed about the Pharasees doing.
There are many problems with doing this.
1) We are not God, and should not be vain enough to decide we can "expand" on God's law.
2) We end up spending so much time trying to catch other people in a sin-against-man-man-law that we ignore the commandments from Christ to love one another, to forgive one another, to judge not lest we be judged.....
If you feel that a beach is a temptation to you, then by all means, avoid the beach, however, don't fool yourself into thinking the problem is the beach. The problem is your own lustful thoughts, and you should work on your heart to change your susceptibility rather than just hope you can avoid temptation all your life.
Another problem with this thinking is that there is no end to the list that can be made. Certain churches prohibit any kind of instrumental music in their halls because someone decided that even a piano is sinful. Others decided that if they danced they had lustful thoughts. Where do you draw that line? Is a woman in a skirt or a woman in pants more likely to entice one particular person to sin? If you are sexually attracted to people of a certain hair-color, or build, are you going to avoid places where you might encounter them?
How are you going to find the lost and wittness to them if you lock yourself in a room and never meet them?
The answer is to get so close to God, via prayer and bible study - that you know He will guide you through temptation.
(KJV) Mark 7:6 He answered and said unto them, Well hath Esaias prophesied of you hypocrites, as it is written, This people honoureth me with their lips, but their heart is far from me. 7 Howbeit in vain do they worship me, teaching for doctrines the commandments of men. 8 For laying aside the commandment of God, ye hold the tradition of men, as the washing of pots and cups: and many other such like things ye do. 9 And he said unto them, Full well ye reject the commandment of God, that ye may keep your own tradition.
Or RSV 6 And he said to them, "Well did Isaiah prophesy of you hypocrites, as it is written, 'This people honors me with their lips, but their heart is far from me; 7 in vain do they worship me, teaching as doctrines the precepts of men.' 8 You leave the commandment of God, and hold fast the tradition of men." 9 And he said to them, "You have a fine way of rejecting the commandment of God, in order to keep your tradition!